San Luis Obispo ~ Coalition of Appropriate Technology’s Guide to
Ha rvestin g th e Ra in
Port San Luis Light House built in 1890 utilizes an
impervious surface to collect rainwater which gravity
feeds underground concrete storage tanks seen here.
This Los Osos residence captures rainwater from the
roof with a downspout diverter. Harvested rainwater is
used for landscape irrigation.
The California Conservation Corps installed a large
rainwater harvesting system on their campus behind
Cuesta College. This metal collection tank is capable of
holding 30,000 gallons, which feeds their nursery.
A series of wood wine barrels capture water for
landscape irrigation in the dry season at Camp Ocean
Pines in Cambria. Overflow from the barrels and the
downspouts are directed to a rain-garden.
Storage and Use
For San Luis Obispo and Santa Barbara County
Suggested donation: $10.00
appropriate technology
sustainable planning
green architecture
San Luis Sustainability Group
Funding for this project has been provided in part by the Morro Bay National Estuary Program with funding
from the U. S. Environmental Protection Agency, SLO-COAT members, individual companies shown above
and the City of Santa Barbara.
This is the third publication in an educational series regarding water and waste applications of appropriate
technology for San Luis Obispo County and now Santa Barbara County as well.
These guidelines are being developed by the San Luis Obispo Coalition of Appropriate Technology (SLOCOAT) to specifically address efforts to maintain a healthy hydrological cycle throughout the Central Coast.
SLO-COAT is a joint effort of SLO Green Build, the San Luis Bay Chapter of the Surfrider Foundation, SLO
Permaculture Guild and the Santa Lucia Chapter of the Sierra Club. The information presented is for general
education purposes. Final details and construction must be developed and designed for specific site
conditions; therefore SLO-COAT is hereby indemnified from any liability arising from the use of this
information.
Cover image- photo credits: Port San Luis Lighthouse cistern- San Luis Sustainability Group, Los Osos residential rain
barrels- Lawson Schaller, California Conservation Corps Cistern at Cuesta College - Alex Vincent, Rain barrels and rain
garden at Ocean Pines Camp cabins in Cambria - San Luis Sustainability Group.
San Luis Obispo Coalition of Appropriate Technology’s
Guide to
Harvesting the Rain: Storage and Use
© June 2013
Appropriate technology is defined as applying technology to
address problems related to energy use, the water cycle, and
affordable building at the smallest and most accessible scale
possible.
The water imbalances in San Luis Obispo and Santa Barbara
Counties have become evident as many municipalities implement
water rationing policies. Growth has always been naturally
restrained due to the scarcity of water resources in our counties.
New development is often burdened with the subsequent increase
in infrastructure costs. Fortunately, over the past thirty years, the
research and refinement of appropriate technologies as related to
water have much to offer us today.
SLO-COAT believes it is imperative that we revisit, at a local scale,
the encouragement and application of appropriate technology. Both
counties are in a position to be at the forefront of these efforts to
reconcile growth and environmental quality.
Application of appropriate technologies as described in this guide
can improve our connection to water and maintenance of a healthy
hydrologic cycle. Key terms appear in bold italic and are defined in
the glossary at the end of this guide. In addition to Harvesting the
Rain, appropriate technology topics related to healthy watersheds
and water cycles are:
Graywater
Rainwater Management for Low Impact Development (LID)
Waterless Waste Treatment
Look for more information and educational events presented by
SLO-COAT on these topics. If you would like to become involved,
find SLO Green Build online at www.slogreenbuild.org
Contributing authors of SLO-COAT: Ken Haggard- Architect & Planner San
Luis Sustainability Group, Mikel Robertson- General Contractor & Green
Building Material Specialist Green Goods, Rachel Aljilani- LEED AP, Alex
Vincent- Permaculture Designer.
Special Thanks to:
Brad Landcaster, Art Ludwig, Brock Dolman, Nate Downey, Mark Lakeman
and Johnathan Todd who have helped educate our community on the
current trends in appropriate technology applications and regulations. This
would not be possible without the ongoing support of SLO-COAT members
and peer reviewers: Mladen Bandov, Andrew Christie, Lawson Schaller,
Joshua Carmichael, Pat Renshaw, Teresa Lees and the numerous
community members also concerned about water resources and
sustainable development.
PACIFIC OCEAN
CUESTA RIDGE
HIGHEST
RAINFALL
evaporation
COASTAL WATERSHED
fog condensation
CAMBRIA
CAYUCOS
salt water intrusion
precipitaion
Green Valley, Los Osos Valley, Chorro Valley, Edna Valley,
Arroyo Grande, Huasna Valley, Nipomo Valley, Cuyama &
Santa Maria Rivers
LOS
OSOS
MORRO SAN LUIS OBISPO
BAY
aquifer recharge
aquifer recharge
WEST TO EAST SECTION
NATURAL HYDROLOGIC CYCLE
No matter where you live, you live in a watershed, and are part of a hydrologic cycle. A natural hydrologic
cycle and healthy watershed work hand in hand to create a clean, healthy environment that supports
complex social, economic and ecological systems.
A watershed is a basin that funnels water from ridge tops to the ocean. The hydrologic cycle occurs in a
watershed and provides fresh water in the form of precipitation (rain, hail, snow) and condensation (fog).
Water collects in riparian areas forming creeks and streams, and infiltrates into the ground replenishing
aquifers. An aquifer is an underground layer of rock or soil in which groundwater resides. Aquifers can
provide substantial amounts of potable water but many are overdrawn.
WATER RESOURCES- AVAILABILITY CONCERNS
Water availability in our two counties is a serious problem. Without creative responses on all of our parts, it
is destined to become worse due to climate change, seasonal irregularities and population growth. Already
several of our communities are impacted by these problems like Cambria, Nipomo and Los Osos. With
continued drought cycles, this number will increase substantially.
Rainwater harvesting is a way to stretch a county’s natural water budget and can be a big part of being
more creative with our limited water resources. Most people don’t realize how much effect rainwater
harvesting can have even in the dryer parts of our county until they do the simple calculations illustrated on
page 2 of this guide. By collecting and storing rainwater we can reduce rapid pollutant filled run-off into
our oceans and creeks and reduce our water demand from remote sources during dry periods.
I
SAN
CARRIZO PLAIN ANDREAS
FAULT
SALINAS RIVER
RAINFALL
LOWEST
RAINFALL
GRADIENT
precipitaion
INLAND WATERSHED
CLOSED WATERSHED
SALINAS VALLEY
CARRIZO PLAIN
SODA LAKE
ATASCADERO
SAN MIGUEL
PASO
ROBLES
aquifer recharge
THROUGH SAN LUIS OBISPO COUNTY
non-potable
water
BENEFITS OF HARVESTING THE RAIN
1. Reduce the water bill for your home or business
2. Capture water for passive & active landscape irrigation
3. Add aesthetic interest to your yard
4. Protect your community’s wildlife, soils, creeks, lakes & watersheds
5. Help your community by reducing off-site flooding problems and reducing the
extent of municipal stormwater infrastructure; thereby saving public funds
6. Reduce pollution entering the surface waters
7. Recharge groundwater aquifers
Santa Barbara (SB) County has a similar profile section as the one shown above for San Luis Obispo
(SLO) County. Wet areas along the coast are separated by mountains form a progression of drier valleys
as one proceeds inland. For example, the Santa Ynez Valley is similar to the leeward side of the Cuesta
Grade and the Cuyama Valley greatly resembles the Carrizo Plain.
II
WHAT IS RAINWATER HARVESTING?
The long history of rainwater collection, can be traced (in recorded
history) as far back as ancient times some 3,000 years ago (850 BC) if
not even farther. Yet today, as long as water is not a problem, people
don’t really seem to care where it comes from or even how it gets into
the house, just as long as it is there and useful.
When we develop communities, we create impervious areas which
inhibit the absorption of rainwater into the ground and local aquifer. It
also diverts water that once made its way to a creek or stream.
Although the increase in impervious surfaces creates difficulties such
as increased water run-off during storms, this doesn’t need to be the
case. Rainwater harvesting is perfect for pairing with impervious
surfaces if those surfaces are adequate for becoming rainwater
collection components.
If the history of rainwater collection tells us anything of value, it is that
filtration is the most important component in any harvesting system.
Different collection surfaces and environments allow you to catch water
of various qualities. Understanding which contaminants might be in the
water you harvest and how to filter it for the intended use are
necessary for health and safety.
Rainwater harvesting regulations will vary in urban and rural settings.
Be sure to double check with your local building and health
departments to make sure you can use your rainwater for the intended
use. Rainwater is used in both potable and non-potable uses within the
county, but potable uses require extensive filtering, treatment and
engineering whereas non-potable uses such as landscape irrigation
systems often require less filtering and treatment.
Contact information is located on the back cover of this publication to
assist you in connecting with your local jurisdiction to make sure you
have a safe and healthy rainwater harvesting experience.
III
Rainwater:
Problem or Resource?
The first heavy rainfall brings a first
flush of non-point source
pollution as illustrated by the
outfall pictured below along the
E m b a r c a d e r o i n M o r r o B a y.
Samples and testing analysis
conducted by the Morro Bay
National Estuary Program showed
E. coli levels varied in 2009 from
1,223 to 7,701 MPN/100 mL. The
standard for safe swimming is 235
MPN/100 mL. Capturing rainwater
and using it on site helps reduce
the amount of rainwater that enters
storm-water management systems,
like curbs and gutters that drain to
the ocean.
Harvesting rainwater can effectively
reduce the density of pollutants at
first flush locations by reducing the
quantity of stormwater that carries
bacteria, heavy metals from cars,
pesticides, pet waste and other
non-point source pollutants that
make their way via stormwater into
sensitive aquatic habitats, such as
estuaries, streams and the oceans.
In addition, rainwater harvesting
restores some of the filtration that
occurs in natural environments that
is lost by development.
TABLE OF CONTENTS
STEP 1: Baseline Conservation
1
STEP 2: Calculating Rainwater Harvesting Potential
2-4
STEP 3: General Design Considerations
5
Regulations and Small Scale Rainwater Harvesting Systems
6
Large Scale Rainwater Harvesting Systems
7-8
I. Collection Components
1. Collection Surfaces
9-10
2. Gutters
11-12
3. Downspout Diverters
12
II. Cleaning Components
4. First Flush Devices
13
5. Filters
14
III. Storage Components
6. Storage Tanks
15-17
7. Mosquito Screens
17
IV. Use Components
8. Water level indicators
18
9. Pumps, Access Pipe & Auto-fill
18
10. Treatment (UV Filters)
18
Glossary
19
Product Resources
20
STEP 1: BASELINE CONSERVATION
Before incorporating rainwater into your
lifestyle, first start off by adopting a baseline
conservation plan. Conservation is the most
affordable technology and practices are
readily available that require little if any
behavior change. Most water providers
have programs to help you conserve by
offering free or discounted low flow shower
heads, faucet aerators, toilet tummies and
more.
Kitchen
Scrape rather than rinse dishes before placing them in the
dishwasher.
Do not thaw frozen food under running water.
When hand washing dishes, fill one basin with soapy water
and the other with rinse water. Avoid running water
continuously while washing dishes.
Install Energy Star rated dishwasher and only wash full loads.
While this document does not attempt to
provide a thorough cost benefit analysis, we
recognize it is a worthwhile consideration.
Costs and benefits will vary greatly
depending on the rainwater system
selected, the local cost of water and volume
utilized. Simple systems are low cost and
can be done by the homeowner with few
new parts and supplies, or by integrating
salvaged or used materials. Other systems
are more complex, requiring professional
installation, and expensive components.
Regardless of the system selected and the
volume utilized, the user will have the
satisfaction and benefit of reusing water,
helping the environment, and having a
drought resistant supply during mandatory
watering restrictions.
Water auditing is an important technique for
determining water usage. It is helpful for
identifying areas where water is being
wasted. Sometimes one small faulty
component in a toilet or irrigation system
could be costing you several gallons of
water each day. Studies estimate leaks
account for 18% of residential water
consumption. Ample resources and training
are available to help you with both indoor
and outdoor water audits. After accounting
for water uses and losses, strategies can be
identified for conserving water which means
lower water bills.
Laundry
Install Energy Star clothes washer and set water volume to
the minimum requirement per load. Use a clothes rack or line
to dry your clothes if possible.
Use short water cycles for lightly soiled loads.
Pre-treat stains to avoid multiple washings.
Soak heavily soiled items in a sink one third full to prewash.
Bathrooms
Check for leaks from pipes and faucets, the smallest drip can
waste up to 2 gallons per day!
Install dual-flush or ultra low flow toilets.
Install low-flow faucets, shower heads and faucet aerators.
Turn off water while brushing your teeth and shaving.
Take 5 minute or shorter showers and turn water off during
and while soaping.
Waterless urinals, composting toilets or dry vaults are very
appropriate and becoming legal and applicable.
Outdoors
Use graywater in your landscape like a laundry to landscape
system.
Plant drought tolerant or xeriscape landscapes.
1
STEP 2: CALCULATING RAINWATER HARVESTING POTENTIAL
How Much Rain Can I Expect to Capture?
Los Osos Example:
First, using the rainfall map for San Luis Obispo or Santa
Barbara County on page 3 or a number of on-line weather
data resources, you can determine your average rainfall per
year. For example, Los Osos shows an average rainfall
contour of 18 inches per year on this map. Convert inches
to feet by diving by 12. Los Osos then has an average of
1.5 feet per year of rain.
Then examine your collection surface to determine the area
of collection. For example, if you have a roof surface that is
20 feet by 50 feet than your collection area would be 1,000
square feet.
Now multiply your average rainfall per year by the collection
area. For Los Osos this is 1.5 feet multiplied by 1,000
square feet, so you can collect 1500 cubic feet of water.
To make this number more meaningful in terms of gallons,
you will need to convert cubic feet to gallons. There are
7.48 gallons per cubic foot. So for the Los Osos example,
we’ll multiply 1500 cubic feet by 7.48 gallons per cubic foot
and discover that this relatively small collection area can
capture 11,220 gallons per year.
The other consideration is the water lost by the first flush
device, this is usually 10 gallons for every 1,000 square feet
of collection surface (see page 13). So for our Los Osos
example, we can probably capture 11,205 gallons.
In some areas of SLO County like Adelaide where the
average rainfall is 42 inches per year, rainfall is 2-3 times as
much as Los Osos while in other areas like the California
Valley it is less than half as much, only 8 inches per year.
With a small area of 1,000 square feet, it is possible to
capture anywhere from 5,000- 26,000 gallons of water per
year. Most sites will have much larger collection areas and
much greater potential for harvesting the rain.
Rainwater harvesting can be appreciable, if a large enough
cistern is used in conjunction with baseline conservation
measures, many of the buildings in the Central Coast could
be self-sufficient and operate strictly off rainwater.
2
#1- Convert rainfall to feet per year
18”/ 12 = 1.5’
#2- Calculate collection area
20’ x 50’ = 1,000 ft2
#3- Calculate cubic feet of water
1,000 ft2 x 1.5’ = 1,500 ft3
#4- Convert cubic feet to gallons
1,500 ft3 x 7.48 gal/ft3 = 11,220 gal
#5- Subtract first flush loss
11,220 gal - 15 gal = 11,205 gal
QUICK ESTIMATE:
For simple estimating: for every 1” of
rainfall per 1,000 square feet of
collection area, you can capture 620
gallons of water.
This gives you a quick way to estimate
rainwater capture. To see how far this
amount will go in regard to landscape
irrigation, see the calculations on the
following page. We think you will be
surprised how much can be done.
STEP 2: CALCULATING RAINWATER HARVESTING POTENTIAL
Rainwater can be used for landscape irrigation and, if
properly treated, for indoor non-potable uses such as
toilet flushing. Deciding on how you will use your
harvested rainwater will determine the storage
capacity you need and the correct selection of
pumps, filters, and any other materials.
For landscape irrigation in your yard, determine how
much rainwater you need by evaluating the
landscaped areas where you will use the harvested
rainwater, and then how much rainwater is available
for harvesting.
Annual Rainfall for San Luis Obispo and Santa Barbara Counties
Shown on the right is a map
of rainfall inches per year for
an average year. As can be
seen, the amount of rainfall
aries considerably over
relatively small distances
due to topographical
changes. You can use this
information to calculate your
specific rainwater harvesting
potential as explained on
page 2.
Roof Area Available for
Rainwater Harvesting
A 1,000 Square Feet
B 1,500 Square Feet
C 2,000 Square Feet
Average rainwater available each year for regions within SLO and SB Counties
(total gallons)
North County
[14 Inches]
North Coast
[18 Inches]
South Coast
[18 Inches]
San Luis
Obispo
North County
[13 Inches]
Santa Ynez
Valley
Cuyama
Valley
[8 Inches]
[18 Inches]
[24 Inches]
[18 Inches]
Santa
Barbara
A
7,000
9,000
9,000
12,000
6,000
9,000
4,000
9,000
B
10,000
13,000
13,000
18,000
9,000
13,000
6,000
13,000
C
14,000
18,000
18,000
24,000
13,000
18,000
8,000
18,000
Average rainwater available each year is based on published rainfall intensity data and 80% roof surface capture efficiency.
Source: San Luis Obispo County Department of Public Works dwg #H-4 August 2006 & Hydrology Section, County of Santa Barbara
3
STEP 2: CALCULATING RAINWATER HARVESTING POTENTIAL
Consult a landscape professional or use the following
table as a guide to estimate the water demand for the
landscape planting types and the climate specific to
your location. On California’s Central Coast, the dry
season is typically May through October, which has
very little rainfall. Most of the harvested rainwater is
captured during the wet season and used during the
dry season. For example, a high water landscaped
area of 400 sq. ft. in Santa Barbara could require
6800 gallons during the dry season. A 1,000 sq. ft.
roof could collect 9,000 gallons of water, more than
enough for a thirsty landscape!
Relative Water Demand for Landscape Irrigation for San Luis Obispo and Santa Barbara Counties
Reference
EvapoTranspiration
Zones
1
Coastal Plains Heavy
Fog Belt
3
Coastal Valley & Plains
4
South Coast Inland
Plains
6
Upland Central Coast
10
North Central Plateau &
Central Coast Range
16
Westside San Joaquin
Valley
Landscape planting
A
CA native/adapted
B
Ornamental garden
C
Turf or tropical
(low water needs)
(moderate water needs)
(high water needs)
Typical dry season (May-Oct) total water demand for regions within SLO and SB Counties
(gallons per square foot of landscape area)
North County
[Paso Robles]
[Morro Bay]
[Arroyo Grande]
San Luis
Obispo
North County
[Guadalupe]
Santa Ynez
Valley
Cuyama
Valley
[Cuyama]
Santa
Barbara
North Coast
South Coast
[Santa Ynez]
A
6
5
4
5
5
6
7
4
B
15
11
10
12
11
14
18
11
C
24
18
17
20
18
23
29
17
Total water demand is based on WUCOLS (Water Use Classification of Landscape Species published by the University of California Cooperative Extension, the
Department of Water Resources and the Bureau of Reclamation, 2000.) methodology, using plant factors, irrigation efficiency, and reference evapotranspiration data.
4
STEP 3: GENERAL DESIGN CONSIDERATIONS
I. Collection
1. Roof Surfaces
2. Gutters
II. Cleaning Components
3. Downspout Diverters
4. First Flush Devices
5. Filters
1
2
5
7
6
8
3
III. Storage Components
6. Storage Tank
7. Mosquito Screen
4
IV. Use Components
8. Water Level Indicators
9. Pumps, Access Pipe & Auto-Fill *
10. Treatment
9 10
Overflow
* Not used in most basic systems
Small Scale Rainwater Harvesting
create dust and debris? Can you modify the situation
by planting screening and filtering vegetation? Take
note of birds, squirrels, raccoons, and other wildlife.
What are the local insects? Note local wind patterns.
Get a feeling of all the stuff collecting on your roof
and with each step of the rainwater catchment
system what you need to filter.
There are some basic design considerations to take
into account when combining rainwater system
components. The most important factor is to keep the
water that you collect clean and healthy. In natural
environments there are large amounts of dust,
pollen, animal feces, dead insects, animals and
leaves, but there is also an overwhelming amount of
natural filtering and cleaning that occurs. Most of this
filtering occurs through thatch, leaves, gravels, soils,
etc. This is why streams in their natural state are
almost always clean. Our main goal in designing a
rainwater harvesting system is to replicate what
occurs in nature at the scale of the individual
building. Therefore, all these components must work
together to reduce contaminants and ensure filtration
at many levels.
When using the roof of a house as a catchment
surface, it is important to consider that many roofs
consist of one or more roof “valleys.” A roof valley
occurs where two roof planes meet. A roof valley
concentrates rainfall runoff from two roof planes
before the collected rain reaches a gutter.
Like any system, to keep it healthy requires
maintenance. Annual cleaning before the rainy
season reduces the possibility of clogging and
overflows which can effect the purity of the water.
Make sure to sweep valleys in the roof and take note
of and repair peeling paint, loose shingles and
miscellaneous debris. Clean at flashing locations,
chimneys, vent pipes, satellite dishes, skylights and
other protruding surfaces.
To design a rainwater harvesting system you must
look beyond your roof or catchment surface and
examine the micro-bioregion of your site. Walk
outside and note the location, size and species of
nearby trees. Learn about the fruit, flowers and
leaves that may seasonally drop onto your catchment
area. Ask yourself, does the proximity of the road
5
REGULATIONS & SMALL SCALE RAINWATER HARVESTING SYSTEMS
Building codes and regulations are undergoing
constant change, so it is important to check with your
local jurisdiction before installing any rainwater
harvesting system. California generally allows small
scale residential systems under the plumbing code to
be exempt from permitting if:
that has been treated to a level suitable for those
uses. Backflow prevention and cross connection are
the primary concerns when rainwater is used in
parallel with potable water systems, so additional
measures must be taken to insure separation (see Use
Components, pages 18-19 of this guide).
Numerous resources are out there to help explain
how to build a rainwater harvesting system, but it isn’t
Tanks are supported on grade
a one size fits all system. Every situation will vary
based on the location, collection surfaces, storage
Tanks do not exceed a height-to-width capacity, toxins, allowed uses, etc., so asking an
ratio of 2:1
expert how to go about designing your rainwater
harvesting system is a great idea.
Water is intended for irrigation only
Total capacity does not exceed 250
gallons
Maintenance is a reality with all rainwater systems
regardless of scale, so be prepared to do this yourself
Tanks are labeled with signs for non- or have someone help you with maintaining the
potable water
various components of your system. A quick overview
of maintenance items are presented below:
Non-potable water does not interact with
potable water systems, building sanitary
sewer systems or drainage systems that
flow to a creek
Collection surfaces are clear of debris
Gutters and screens are clear of debris
First flush devices emptied
Rain barrels and smaller capacity tanks can be linked
together to achieve a greater capacity. It is important
to remember to manage overflows properly with both
small and large scale systems. A rain garden or swale
can direct overflow from small systems into planted
areas that provide aesthetic value and help recharge
groundwater (see SLO-COAT Rainwater Management Guide).
Overflow routes are able to accept water
Storage components do not leak
Filter fabrics are not accumulating bacteria
Mosquito and rodent screens are in place
Systems used for irrigation that rely on gravity are the
simplest and will require the least amount of
maintenance and energy. Once you add pumps and
other electrical components to your rainwater
harvesting system, you will likely need building
permits. Even large amounts of grading can require
permits, so please check with your local building
department to help protect yourself and others.
Pumps work properly
Carbon and UV filters are properly
maintained
Non-potable water and rain harvesting
signs are intact
Your storage containers are not full of odd
colored water and foul odors
*Remember, clean water is colorless and odorless
Uses for harvested rainwater and the level of
treatment before use should also be verified with local
officials. Irrigation, car washing, laundry and toilet
flushing needs can be met with non-potable water
Enjoy using your system
6
LARGER SCALE RAINWATER HARVESTING SYSTEMS
Rural Lands
Water Sequence
(1) In-Ground Catchment
(2) Screen & Pre-Filter
(3) Initial Storage
(4) Filtration
(5) Storage Tank & Pump
swale
Three generalized large scale
approaches to rainwater
harvesting are shown here. A
rule of thumb for estimating the
cost of a system is usually $1/
gallon collected, but this will
vary considerable with the scale
and context of your situation.
springs
reservoir
high storage
pump house
swale
For large scale applications with
High-Density Housing significant acreage and large storm
Water Sequence water capture potential, storage in
carefully located reservoirs formed
with ground contours are most cost
effective. The main concern with
these systems is the large losses
due to evaporation, about 10% per
(1) Pre-Filter (2) Tank (3) Pump
week minimum.
(4) Sand Filter (5) Larger Tank
(6) Pump
Reservoir systems should utilize
gravity flow whenever possible.
Historic farms on the central coast
illustrate this principle with the
underground
vertical arrangement of well, pump
tanks
house, storage tank and windmill.
Commercial Lots
No Mixing!
Remember that any system needs to
avoid mixing graywater and
harvested rainwater.
Large commercial situations provide ample
collection surfaces with roofs, parking lots,
plazas, etc. Large underground storage
tanks, pumps and additional filtration and
purification are typical in these systems.
7
In higher density housing, parks,
greenways and roof surfaces can
all become collection surfaces.
This water may be more polluted
and should be restricted to
landscape irrigation. Underground
storage tanks can be placed under
parking lots and driveways, but
need to be rated to avoid damage
from surface loads.
LARGER SCALE RAINWATER HARVESTING SYSTEMS
All reservoirs should consider the following: 1) depth to surface area ratio- a greater depth and less surface
area will reduce the losses from evaporation, 2) erosion and pollution- these should be minimized in the
catchment area, 3) fencing- to keep livestock out and for other safety reasons, 4) gravity fed outlets- reduce
maintenance and increase efficiency of the system. Three approaches to reservoirs are shown below.
Earthen dam: Use of a natural
depression or gully to contain water
held by soil that was graded to make
the basin. Soil type needs to limit
seepage and be capable of carrying the
weight of the dam wall. A clay layer may
need to be added if the soil is too
porous. There should be no ant hills,
pits, sewage outlets, saline or
calcereous soil at the site. Provide two
spillways to prevent damage from
washouts in large storms.
spillway with
rock apron
Groundwater dam: This approach uses
large deposits of sand near a natural
water course to hold the water
underground but near the surface. It can
be enhanced by using a masonry wall
or a subsurface clay dam to build up
sand in a large pocket that can be filled
with run-off water. One advantage is
that surface evaporation is greatly
reduced which is very beneficial during
long dry periods.
silt traps
collected from
reverse side
clay
wall
outlet
pipe
Rock catchment dam: Massive unjointed
rock outcrops can provide excellent
catchments and holding surfaces. Soil
and vegetation on the rocks should be
removed from the rock surfaces and any
large joints or cracks should be sealed
with mortar or bentonite clay. Run-off can
be channeled by rock or concrete gutters
or groves cut into the rock.
reservoir
new level
filter
box
sand pocket
stone or ground gutters
former
level
reservoir utilizing an inselberg
type stone outcrop
spillway
#1
charcoal filtration
to remove bacteria
Use of harvested rainwater
for potability requires
three phases of treatment:
#2
UV light to
kill microbes
#3
fine screening to
remove small particles
Typical underground storage tank for commercial application utilize a plastic tank. These tanks are available in
a variety of sizes and shapes. Alternate large scale cellar systems for holding water under permeable paving is
shown on page 19 of SLO-COAT”S Rainwater Management for Low Impact Development Guide.
From Plazas,
Roads, Roofs,
Parking, Etc.
10
5
5
1
9
2
6
3
To Overflow
4
8
7
7
8
To
Point
of Use
Underground Storage Tank
1. Collection point
2. In-Ground First-Flush Filter
3. Non-Return Valve
4. Smoothing Inlet
5. View & Maintenance Ports
6. Stainless-Steel Suction
Filter Floor
7. Tank hold-Downs
8. Submersible Pump
9. Overflow Valve
10.Pressure Tank
I. COLLECTION COMPONENTS
B. Slate
Slate’s smoothness makes it ideal
for a catchment surface for potable
use, assuming no toxic sealant is
used; however, it is expensive so
cost considerations may preclude
its use.
C. Elastomeric
Elastomeric surfaces are rubber
like and commonly used for sealing
flat roofs that are used for walking
(decks, balconies, etc.).
1. Roofs for Rainwater Collection
1
2
D. Clay or Concrete Tile
Clay and concrete tiles are both
porous and easily available
materials that are suitable for
potable or non-potable systems.
They may, however, contribute to
small water loss due to texture,
inefficient flow, or evaporation. To reduce water loss
and prevent bacterial growth on porous materials,
tiles can be painted or coated with a sealant, which
may also contain toxins that leech into the water.
The roof of a building is the first choice for collection.
Water quality from different roofs is a function of the
type of materials and local micro-climate conditions.
Roof surfaces come in two general types, impervious
to water and permeable surfaces of various degrees.
Impervious roofs are the most desirable for rainwater
collection because permeable roofs are more likely to
collect dust and debris and are more difficult to clean.
It is important to minimize any dirt, debris or
chemicals that could contaminate the water so that
filtration can be minimized later in the process. Below
we list various types of roof surface in order of their
suitability for rainwater collection:
E. Living or Green Roofs
Earthen roods planted with a variety of plants,
succulents, grasses and flowers help cool a roof and
create social space. Subsurface cells allow additional
drainage during heavy rain periods and divert water to
gutter sources.
A. Metal
The quantity of rainwater that can be collected from a
roof is in part a function of the roof texture, the
smoother the better. A commonly used roofing
material for rainwater harvesting is sold under the
trade name Galvalume®, a 55 percent aluminum/45
percent zinc alloy- coated sheet steel. Galvalume® is
also available with a baked enamel coating, or it can
be painted with epoxy paint. Some caution should be
exercised regarding roof components. Roofs with
copper flashings can cause discoloration of porcelain
fixtures and is not desirable for potable uses.
F. Composite or Asphalt Shingle
Due to leaching of toxins,
composite shingles are not
appropriate for potable systems,
but can be used to collect water for
irrigation. Composite roofs have an
approximate 10-percent loss due to inefficient flow or
evaporation.
Standing Seam
Ribbed
Corrugated
Photo Credits:
1 Mystic Grey Slate Roof in Canada, Westone Slate
2 Elastomeric Roof, Michael R. Allen
9
I. COLLECTION COMPONENTS
G. Tar or Gravel
A built up roof consisting of layers
of tar and gravel are a commonly
used surface on low slope roofs.
Due to potential toxins in the tar
and the debris-holding and flaking
characteristics, this type of roof along with composite
roofs is not recommended for potable systems. These
roofs have an even higher loss rate due to inefficient
flow and evaporation.
Alternative Materials
With the ever increasing demand
for “Green Building Products”, new
materials are emerging containing
recycled content and rapidly
renewable materials that are nontoxic and have a lower embodied energy. One such
example is rubber roof tiles made from old tires.
Toxicity of such materials need to be checked before
water is to be used for purposes other than irrigation.
H. Wood Shingles or Shakes
Wood shingles are not very
desirable for water collection due to
their short life span. They also are
capable of producing a lot of debris
3
and can harbor mold. Fire
protection requirements also restrict their use in high
fire severity zones. Treatments to protect the shingles
from fire are often very toxic with high VOC levels and
will add contaminants to the water running off of them.
Other Collection Surfaces
Beyond your building’s roof, one can collect rainwater
from other structures, decks and paved areas. In
urban areas, plazas, parks, and parking lots have
been used for water collection. Debris in the form of
trash and toxic drippings from cars make filtration and
treatment much more important in these cases.
Photovoltaic systems, either on roofs or stand-alone,
also act as excellent collection surfaces.
Roof Surface Comparison Table
This table compares various collection surfaces and gives a relative rating for the attributes listed.
+ = less, ++ = more, +++ = most,
Collection Surface
$ = least expensive, $$ = more expensive $$$ = most expensive
Collection
Efficiency
Potable
Options
Expected
Life
Flammable
Cost
Absorbs
Pollutants
Metal Seam
+++
Yes
+++
No
$$$
No
Corrugated Metal
+++
Yes
+++
No
$$
No
Natural Slate
++
Yes
+++
No
$$$
Yes
Elastomeric Roof
+++
Yes
+++
Yes
$$$
No
Clay or Concrete Tile
+
Yes
++
No
$$
Yes
Living or Green Roof
+
No
++
No
$$$
Yes
Asphalt Shingle
+
No
+
Yes
$
Yes
Tar & Gravel
+
No
+
Yes
$
Yes
Wood or Shingle Shake
+
No
++
Yes
$$
Yes
Plastic Tile
++
Yes
++
Yes
$$$
No
Photo Credits:
3 Shake Roof in Romania, Teveten
10
I. COLLECTION COMPONENTS
2. Gutters
Gutters are installed to capture rainwater running off the
eaves of a building. Gutters are important to protect the
critical juncture between walls and roofs from water damage
and are an integral part of any rainwater harvesting system.
The most common materials for gutters and downspouts are
galvanized steel, aluminum or PVC plastic. Many gutter
installers provide seamless extruded aluminum gutters which
have the advantage of not requiring waterproofing of joints in
long runs.
Gutter Schematic
roof
roof edge flashing
gutter support
gutter
drop outlet
downspout
downspout support
Watch out! For potable water systems, lead cannot be used
in gutter solders as is sometimes the case in older metal
gutters. The slightly acidic quality of rain can dissolve lead
and contaminate the water supply.
Other necessary components of a good gutter system are the
drop outlet, which routes water from the gutters downward
and 45 degree elbows which allow the downspout pipe to fit
snug to the side of the building and brackets and straps to
fasten the gutters and downspouts to the fascia and wall.
Gutters must be installed to slope toward the downspouts.
The greater the slope the less likely of clogging so again it’s
best not to have too long a gutter served by the downspout.
Also the outside face of the gutter should be lower than the
inside face to encourage drainage away from the building
wall. Maintenance is very important because build up of
debris in the gutter will reduce capacity and put additional
gravity loads on the gutter which could result in sagging and
overflow. Strategies to minimize overflow includes
modification of the size and configuration of gutters and the
addition of more drop outlets. Water diverters on part of the
roof can sometimes be used to increase collection efficiency
for the gutter.
Two of the most standard commercially available gutters are
shown on the right. Custom larger size gutters are relatively
easy to construct and can solve several problems.
Maintenance is easier with a larger cross-section. They are
easier to clean and have less blockage and clogging. Their
greater capacity allows for more space between drop outlets
and downspouts making connections to holding tanks easier.
However, larger gutters require more structural support so
the support system must be carefully designed.
11
5-1/4”
3-3/4”
3-1/4”
Standard Ogee or
K-style Gutter
capacity 0.11 cu.ft./linear ft.
0.82 gal./linear ft.
5-8”
5-8”
Standard Half Round Gutter
capacity 0.17 cu.ft./linear ft.
1.27 gal./linear ft.
Custom Large Gutter
I. COLLECTION COMPONENTS
Gutter Screens
3. Downspout Diverters
A critical element in any rainwater harvesting system
is continual filtration of debris. Your gutter system
offers the first opportunity to begin this sequence of
filtration by the use of screens at the top of the gutter.
Besides providing the first level of filtration, screens
will help maintain flow in an area that often is the
weak link in the maintenance of a rainwater
harvesting system because the inside of gutters are
out of reach and thus too often out of mind. These
gutter screens are a very inexpensive item for the
value given.
Downspout diverters are devices that add to our
multiple filtration objective by filtering rainwater while
diverting water to the storage.
Three types are
shown below:
A. Leaf Screen
The most common approach is to
provide a 1/4 inch screen on the
top of the gutter to catch leaves in
a location that is much easier to
remove than digging them out of
the bottom of the gutter. Leaf screens are usually only
necessary in locations with tree overhangs. Screens
must be regularly cleaned to be effective. If not
maintained, leaf screens can become clogged and
prevent rainwater from flowing into the tank. Built-up
leaves can decay and harbor bacteria.
B. Debris Screen
This is a commercially available
item consisting of a frame with a
relatively fine mesh that fits on the
top of the standard gutter. The
mesh is fine enough to collect most
smaller debris yet does not impede the passage of
water. Cleaning is easy because all one has to do is
hose off the surface using a high pressure nozzle on a
garden hose.
Maintaining Gutter Systems
A “leaf eater” is a screened
collection box at the
interface between the drop
outlet and the down spout
where the debris is
concentrated and is easy to
reach.
A downspout filter consists
of a PVC or stainless steel
cage cut into the spout at a
height slightly above the
highest water level of the
tank. The screen is cut into
the shape of a funnel that
can be easily removed for
inspection and cleaning.
This downspout diverter
has an integral leaf
eater inline. Debris is
diverter with a comb like
device and a mesh
screen. The diverter can
be manually switched
off to allow overflow to
continue down the
downspout to the rain
garden.
Another approach is a strainer basket in a spherical
shape than can slip into the drop outlet of the
downspout or a cylinder of rolled screen inserted into
the drop outlet. Both of these approaches have the
difficulty of not being easy to get to for regular
inspection and maintenance.
Another simple inline filtration system consists of a
filter sock of nylon mesh than can be installed on the
inlet pipe at the storage tank. This will require
maintenance and needs to be installed without
creating gaps that allow access for animals or insects
that are attracted to water.
Maintenance of your gutter system is important.
Clean gutter screens before the rainy season and
check for overflow during winter storms. Repair
leaks and holes and look for low spots or sagging
areas.
12
II. CLEANING COMPONENTS
A simple homemade first flush
device can be various lengths
depending on the diameter of
pipe used and amount of
diverted water desired. If you
use a 3” diameter pipe, 33” will
hold one gallon. A 4” pipe will
hold the same amount with
only 18” of length and so on.
Roof Washers
4. First Flush Devices
While gutter screens remove the larger debris such
as leaves, twigs and blooms that fall on the roof, a
first flush device gives the system a chance to rid
itself of smaller contaminates such as dust, pollen
and bird and rodent feces. The first flush device
routes flow of water from the first rain storm from the
catchment surface away from the storage tank. The
flushed water can be routed to a planted area.
The volume of rainwater to divert to the first flush
systems depends on the number of dry days
preceding the storm and the local conditions
mentioned earlier. one rule of thumb for first flush
diversion is to divert a minimum of 10 gallons for
every 1,000 sq. ft. of collection surface.
The simplest first flush device is a PVC or meta
standpipe in line with the downspout before the pipe
to the storage tank. This standpipe fills with water
during a rainfall event and redirects water to the tank
after it is full.
The standpipe can be drained
continuously via a pin hole in the bottom or by leaving
the screw closure at the bottom slightly loose.
There are now several
commercial first flush devices
available. The
dependable
ball and seat system works
with a floating ball that seals
the flush chamber after the
chamber fills.
This simple
system is automatic and does
not rely on mechanical parts
or manual intervention except
for occasional cleaning of
settled debris in the chamber.
13
A more elaborate commercially available inline
cleaning system is called the “roof washer.” It is
placed just ahead of the storage tank, filters small
debris for potable systems and also for systems using
drip irrigation. Roof washers consist of a tank, usually
between 30-50 gallon capacity, with leaf strainers and
a 30-micron filter.
All roof washers must be cleaned. Without proper
maintenance they not only become clogged and
restrict the flow of rainwater, but may become
breeding grounds for pathogens. The box roof washer
is a commercially available component consisting of a
fiberglass box with one or two 30-micron canister
filters (handling rainwater from 1,500-3,500 squarefoot catchments). The box is placed atop a ladder-like
stand beside the tank, from which the system owner
accesses the box for cleaning via the ladder.
5. Filters
Pot Filters
A pot filter is the simplest rainwater pre-filter and is
composed of a flanged plastic tray with a perforated
bottom that covers the top of a large basin with a side
outlet. A filter pad is placed over the perforations, the
pad is covered with gravel, and the outlet is piped to
a rainwater tank. Water from a downspout dumps
onto the gravel which strains out leaves and coarse
debris and then flows through the filter mat which
retains solid particles as small as 1/64”. With minimal
maintenance, a pot filter can capture and filter 100%
of the rainwater from a single residential downspout.
Normally pot filters are buried so that the top is flush
with the ground surface, but they can be used above
ground.
II. CLEANING COMPONENTS
Basket Filters
A basket filter consists of a large screened filter basket that
fits within a plastic filter body. Water flows in through a top
port, down through the basket, and out through a bottom
port. A second port is provided at the top to allow overflow
should the filter basket become full. A small basket filter can
filter 100% of the rainwater from roofs up to 5,000 square
feet, with a larger basket filter all do the rainwater from roofs
up to 12,000 square feet. For both, the buried basket system
is easily accessible through a removable manhole cover.
Cascade Filters
In contrast with basket filters, cascade filters do not collect
debris, but rather allow it to wash through the filter in order to
minimize maintenance. This is achieved at the penalty of
lower recovery rates, typically 95% depending on average
rainfall intensity. Rainwater flows in through the top port and
cascades over a curved, multi-level screened filter element
positioned horizontally within a plastic filter body. Filtered
water exits through one bottom port; debris is washed down
the surface of the filter element and exits through a second
bottom port. The filter element, buried underground, is easily
accessible through a removable manhole cover, like the pot
and basket filters.
Also available are internal cascade filters that fit completely
within the access dome of some rainwater tanks. This
compact filter is suitable for roofs up to 5,000 square feet.
Vortex Filters
Like cascade filters, vortex filters do not collect debris, but
rather allow it to wash through the filter in order to minimize
maintenance. Instead of a horizontal filter element, they
utilize a vertical filter element. Rainwater flows in through the
top port, spins around the circumference of the filter body,
and spills into the top of the filter element. A capillary effect
draws water through the side walls of the filter element and
this filtered water exits through the upper side port. Debris
washes down, passes through the open bottom of the filter
element, and exits through the lower bottom port. This design
requires very little maintenance, but at the penalty of reduced
capture efficiency, typically 85% to 90% depending on
average rainfall intensity
14
removed for
cleaning
Pot Filter
removed for
cleaning
Basket Filter
removed for
cleaning
Cascade
Filter
Vortex Filter
self-cleaning
III. STORAGE COMPONENTS
stability of the soil supporting the full cistern weight.
The pad or bed should be checked after intense
rainfall events.
Metal
Galvanized sheet metal tanks are
an attractive option for the urban or
suburban garden. They are
available in sizes from 150 to
2,500 gallons, and are lightweight
and easy to relocate. Tanks can be
lined for potable use. Most tanks are corrugated
galvanized steel dipped in hot zinc for corrosion
resistance. They are lined with a food-grade liner or
coated on the inside with epoxy paint. The paint,
which also extends the life of the metal, must be FDAand NSF-approved for potability.
6. Storage Tanks
Storage tanks sit below the water source, with the
inlet lower than the lowest downspout. Tanks should
be located as close to supply and demand points as
possible and protected from direct sunlight. They can
be placed above ground or below ground, though to
ease the load on the pump, tanks should be placed
as high as practicable.
Storage tanks must be
opaque, either upon purchase or painted later, to
inhibit algae growth. For potable systems, storage
tanks must never have been used to store toxic
materials. Tanks must be covered, vents screened to
discourage mosquitos and animals and those used
for potable systems must be accessible for cleaning.
Fiberglass
Fiberglass tanks are built in
standard capacities from 50
gallons to 15,000 gallons in both
vertical and low-horizontal cylinder
configurations. Fiberglass tanks
under 1,000 gallons are expensive
for their capacity. Tanks for potable use should have a
USDA- approved food-grade resin lining and the tank
should be opaque to inhibit algae growth. Fiberglass
durability has been tested and proven, however, they
are vulnerable to wildfires. The fittings on fiberglass
tanks are an integral part of the tank, eliminating the
potential problem of leaking.
Water runoff should not enter septic system drainfields, and any tank overflow and drainage should be
routed so that it does not affect the foundation of the
tanks or any other structures. To ensure a safe water
supply, underground tanks should be located at least
50 feet away from animal stables or above-ground
application of treated wastewater. If supplemental
hauled water might be needed, tank placement
should also take into consideration accessibility by a
water truck, preferably near a driveway or roadway.
Wood
1
For aesthetic appeal, a wood tank
is a desirable choice for urban and
suburban rainwater harvesters.
Wood tanks, similar to wood water
towers at railroad depots, were
historically made of redwood.
Modern wood tanks are usually of pine, cedar, or
cypress wrapped with steel tension cables, and lined
with plastic. The main disadvantage of these tanks is
that they shrink when dry and can develop leaks
unless continually filled. Even with a liner, the wood
will lose structural strength when the wood shrinks.
For potable use, a food-grade liner must be used.
Water weighs just over 8 pounds per gallon, so even
a relatively small 1,500- gallon tank will weigh 12,400
pounds. Therefore, tanks should be placed on a
stable, level pad. If the bed consists of a stable
substrate, a load of sand or pea gravel covering the
bed may be sufficient preparation. Otherwise, a
concrete pad should be constructed. When the
condition of the soil is unknown, enlisting the services
of a structural engineer may be in order to ensure the
Photo Credits:
1 Beaumont Kansas Water Tower, MadameGraffigny
15
III. STORAGE COMPONENTS
Polypropylene
Polypropylene tanks are commonly
sold at farm and ranch supply
retailers for all manner of storage
uses. Standard tanks must be
installed above ground. For buried
installation, specially reinforced
tanks are necessary to withstand soil expansion and
contraction. They are relatively inexpensive and
durable, lightweight, and long lasting. Polypropylene
tanks are available in capacities from 50 to 10,000
gallons. Low-profile 5,000-gallon polypropylene tanks
do not retain paint well, so it is necessary to find offthe- shelf tanks manufactured with opaque plastic.
The fittings of these tanks are aftermarket
modifications. Although easy to plumb, the bulkhead
fittings might be subject to leakage.
Other types of prefabricated concrete tanks include
new septic tanks, conduit stood on end, and tanks
constructed of concrete blocks. These tanks are
fabricated off-site and dropped into place.
Concrete may be prone to cracking and leaking,
especially in underground tanks in clay soil. Leaks
can be easily repaired although the tank may need to
be drained to make the repair. Involving the expertise
of a structural engineer to determine the size and
spacing of reinforcing steel to match the structural
loads of a poured-in-place concrete cistern is highly
recommended. A product that repairs leaks in
concrete tanks, Xypex, is now also available and
approved for potable use. One possible advantage of
concrete tanks is a desirable taste imparted to the
water by calcium in the concrete being dissolved by
the slightly acidic rainwater. For potable systems, it is
essential that the interior of the tank be plastered with
a high-quality material approved for potable use.
3
Customized tanks are increasingly available that are more
aesthetically adaptable to match a garden space.
In-ground Polypropylene
Some polypropylene tanks are buried for aesthetic or
space-saving reasons. However, in-ground tanks are
more costly to install because of the cost of
excavation and a more heavily reinforced tank. For
installation deeper than 2 feet, the walls of the tank
must be thicker and sometimes an interior bracing
structure must be added. Burying a tank in clay is not
recommended because of the expansion/contraction
cycles of clay soil.
Concrete
Concrete tanks are either poured
in place or prefabricated. Pouredin-place tanks can be integrated
into new construction under a
patio, or a basement, and their
placement is mostly permanent.
Photo Credits:
2 Underfloor Cistern, Stefan-XP
3 Frank Gallagher, www.allindustrialarts.com
2
16
Ferrocement tanks can be customized to a variety of
shapes and sizes and therefore can become a
compositional element in any landscape.
Ferrocement
Ferrocement is a low-cost steel and mortar composite
material. For purposes of this manual, GuniteTM and
ShotcreteTM type will be classified as ferrocements,
which involve application of the concrete and mortar
under pressure from a gun. Gunite, often used for
swimming pool construction, is a method in which the
dry mortar is mixed with water at the nozzle.
Shotcrete uses a similar application, but the mixture is
a prepared slurry. Both methods are cost-effective for
larger storage tanks.
IV. STORAGE COMPONENTS
where it is mandatory), specialized tanks have been
developed that are visually compatible to architectural
and landscape situations such as the slimline tank
series.
Ferrocement tanks consist of an armature made from
a grid of steel reinforcing rods tied together with wire
around which a wire form with closely spaced layers
of mesh, such as expanded metal lath is placed. A
concrete-sand-water mixture is applied over the form
and allowed to cure. It is important to ensure that the
ferrocement mix does not contain any toxic
constituents. Painting above-ground tanks a light
color will help to reflect the sun’s rays, reduce
evaporation, and keep the water cool.
Tank Maintenance
All tanks eventually build up a sludge layer on the
bottom of the tank. It comes from leaves, dirt, and
other debris that washes from your roof and is
carried by the water into your tank. Because the
sludge can be a breeding ground for microorganisms, this layer needs to be cleaned out
regularly. For people who maintain their roofs and
gutters, the tank may only need to be cleaned out
every three years. For those that are less diligent
about maintaining their catchment system, tanks
should be cleaned out at least once a year.
Ferrocement structures have commonly been used
for water storage construction in developing countries
due to low cost and availability of materials. Small
cracks and leaks can easily be repaired with a
mixture of cement and water applied where wet spots
appear on the tank’s exterior. Because walls can be
as thin as 1 inch, a ferrocement tank uses less
material than concrete tanks, and thus can be less
expensive.
7. Mosquito and Animal Screens
Mosquito screens and tight- fitting tank lids prevent
mosquito breeding, and keep water-seeking animals
from fouling the tank. Screens and filters should be
checked and cleaned regularly.
Specialty Tanks
With the wide variety of applications of rainwater
harvesting worldwide (including places like Australia
Tank Material Comparison Table
The table below compares various storage materials and their relative characteristics.
+ = less, ++ = more, +++ = most
$ = least expensive, $$ = more expensive $$$ = most expensive
Cost
Flammable
Capacity
Modular
Available
Aboveground (A)
Belowground (B)
Metal
$$
No
++
Yes
A
Fiberglass
$$
Yes
++
Yes
A/B
Wood
$$$
Yes
+
Yes
A
$
Yes
+
Yes
A/B
$$$
No
+++
Yes
A/B
Ferrocement
$
No
+
No
A
Earthen
$$
No
+++
No
A/B
EPDM
$$$
Yes
+++
Yes
A/B
Storage Material
Polypropylene
Concrete & Masonry
17
IV. USE COMPONENTS
8. Water Level Indicators
Water level indicators can be simple
mechanical pulley and counter
weight systems or more complex
electronic systems. These systems
will be tied to your auto-fill device if
the tank has a supplemental
water level indicator
water supply system. For short
tanks and rain barrels, a mechanical level indicator
will be the most cost effective and easy to calibrate.
Pneumatic water level indicators allow for remote
sensing and can be installed in below ground
situations with water levels up to 8’ deep. Wireless
ultrasonic devices can be located at great distances
from the tanks (1000 ft.) and can have more
sophisticated controls for digitally operating pumps
and electric valves. Digital level indicators can work
with tanks or greater depth, but are not
recommended for steel or modular underground
tanks because of radio-frequency interference.
9. Pumps, Access Pipe & Auto-Fill Devices
Float switches and fill valves can
be used to fill a tank or engage a
pump when the tank has a
specific amount of water in it.
Although gravity flow can be used
for flood irrigation, most other
float switch
rainwater uses require pumping. Submersible pumps
are installed within a rainwater storage tank, but most
require a pump controller that cannot be submerged
or flooded. Surface pumps are typically installed
within a nearby building or pump enclosure. It is
important to keep pump housings out of the sun and
clear of insects.
10. Treatment (UV Filters)
The most important reason for water
treatment is to kill dangerous
bacteria that may be in the water.
Treatment can also improve the
color, odor and taste of your water. A
treatment program may include a
combination of filters, disinfection
UV Sterilizer
with bleach and/or boiling water.
Most illnesses are caused by fecal
bacteria, water test kits detect presence of indicator
bacteria that come from the intestines. If you have the
indicator bacteria in your water that means that you
have fecal bacteria in your water, which are very
harmful and cause disease.
Rainwater from a properly designed rainwater prefiltration and storage system can be used without
further treatment for landscape irrigation, garden
ponds, and most exterior applications. When
rainwater is used within buildings, supplemental
filtration is essential and disinfection is
recommended. For toilet flushing and clothes
washing, a sediment filter will remove suspended
solids which can clog and damage valves, and an
activated-carbon filter will remove dissolved organic
matter which can cause discoloration and odors. For
showering, hand washing, or drinking, use a highintensity ultraviolet sterilizer to kill microorganisms
that could cause illness. All filtration and disinfection
components should be oversized to maximize
performance and minimize maintenance.
Back flow preventers and check valves are important
when systems will require an input of fresh water
either from a well or a local source. There are two
approaches to prevent cross contamination. The first
is to provide a 3” air gap at the fresh water inlet. This
is an actual space of air that exists when the supply
line stops and the water flows through the air before
being added to a storage tank. The other strategy is
to hard line the additional water source with an inline
approved backflow preventer. Municipalities have
Images Courtesy conservationtechnology.com
many concerns about cross contamination through a
siphoning action, so systems require an approved
backflow preventer and require inspection yearly for
proper function. Charges for inspection services will
vary, contact your local authority for more information
on inspections and fees.
Filters used for drinking water are 1-micron filters.
These have very tiny holes and are used to remove
protozoan cysts like Giardia, which chlorine does not
kill. When you are looking for a 1- micron filter look
for a filter that says it removes or reduces cysts. This
is usually used in addition to the sediment filters.
18
GLOSSARY
appropriate technology applying technology to address
problems related to energy use, the water cycle and
affordable building at the smallest, most accessible scale
possible.
irrigation systems key component to any landscape, can
be fed from municipal water sources, wells and even better
water catchment systems. Using rainwater as a primary
irrigation source is a sustainable way to grow a healthy
landscape and helps with overall water conservation.
aquifer the underground layer of rock or soil in which
groundwater resides. Aquifers are replenished or
recharged by surface water percolating through soil. Wells
are drilled into aquifers to extract water for human use.
nonpoint source pollution contamination of a body of
water from a number of sources and locations.
cistern a storage tank or underground reservoir for
rainwater.
potable "Drinking water" or potable water is water of
sufficiently high quality that can be safely consumed or
used domestically.
downspout a vertical pipe that drains water downward
from the gutters.
percolation the movement of water through the soil to the
water table.
drip irrigation system a watering process in which water
flows through tubing and is delivered to plants roots via
emitters or sprayers, rate of water flow is adjustable,
minimizing water runoff and reducing the amount of water
that is lost through evaporation.
permeable ability of water or other liquids to pass through
a surface.
drought tolerant
water.
pervious pavement driveways, walkways and patios
made with gravel, crushed stone, open paving blocks, or
special porous concrete to allow water infiltration.
ability of a plant to survive with little
point source pollution single, identifiable, localized
source of contamination.
erosion control techniques prevent soil loss and water
pollution, can involve the creation of physical barriers, such
as vegetation or rock, to absorb the erosive potential of
wind or water.
pollutant any substance in air, water, or soil that may be
harmful to the health of humans or other living things or
may harm the environment.
evaporation process of liquid water becoming a vapor.
rainbarrel container used to collect and store rainwater.
filtration process of filtering, especially the process of
passing a liquid or gas through a filter in order to remove
solid particles.
rain-garden a planted depression that allows rainwater to
be absorbed and soak into the ground.
rainwater harvesting process of collecting and storing
rainwater or stormwater for beneficial use.
gravity flow use of gravity as opposed to a pump to move
a liquid such as water.
recharge process by which groundwater is absorbed into
the zone of saturation.
greywater / graywater / gray water is water that has been
used in the house and comes from bathroom sinks,
shower, baths and washing machines.
run-off something that drains or flows off, as with rain that
flows off the land.
groundwater water that occupies the pores and crevices
of rock and soil beneath the earth's surface.
soil composed of gravel, sand, silt, clay, organic matter,
gases, and liquid.
gutter channel along a roof’s edge to catch and direct
stormwater.
stormwater run-off rainwater that hits the ground and
flows over the earth’s surface.
hydrologic cycle the natural sequence through which
water passes through the atmosphere as water vapor,
precipitates to earth and returns to teh atmosphere through
evaporation.
surface water water that collects on the ground or in a
stream, river, lake, wetland, or ocean. Shallow trough
between two areas of higher ground.
impervious material that does not allow water or other
liquids to pass through.
watershed area of land that sheds water and directs it
downhill to a particular watercourse or point.
infiltration movement of water through the soil surface into
the soil.
xeriscape environmental design of land using various
methods to minimize the need for supplemental water use
such as using drought-tolerant plants, mulch, and efficient
irrigation to create sustainable landscapes.
19
RAINWATER HARVESTING PRODUCTS & RESOURCES
Aquadra Systems (Edmonds, Washington; distributed by
raintankdepot.com): modular tanks made from 100% postconsumer-recycled, linear low-density polyethylene (LLDPE),
components for connecting several tanks together, and brackets
for securing them to walls.
Aquascape (St. Charles, Illinois; rainxchange.com): belowground storage of rainwater or stormwater with the unusual
feature of allowing use of that stored water in landscape features,
such as fountains and ponds. Storage capacity is created using
AquaBlox module crates that interlock to create large cisterns
made watertight with EPDM liners.
BlueScope Water (San Marcos, Texas; bluescopewater.com):
site-fabricated steel tanks with polymer-composite (Aqualiner)
potable-water-rated liners in sizes from 10,000 to 65,000 gallons,
tanks are available from 1,000 to 5,000 gallons.
BRAE (Oakboro, North Carolina; braewater.com): components for
integrated systems for residential and commercial applications.
Systems available for both potable and non-potable uses,
especially irrigation.
Bushman (Australian company, U.S. operations in Temecula,
California; bushmanusa.com) above-ground polyethylene tanks
for rainwater collection ranging in size from 60 to 2,825 gallons.
Slimline tanks, ranging in size from 130 to 620 gallons, have a
thinner profile to fit against walls, wide range of components.
C o n s e r v a t i o n Te c h n o l o g y ( B a l t i m o r e , M a r y l a n d ;
conservationtechnology.com): wide range of rubber and plastic
materials for water and air-flow management, systems and
components, including pre-filtration, first-flush diverters, tanks,
level indicators, pumps, and water purification.
Invisible Structures (Golden, Colorado; invisiblestructures.com):
Rainstore3 system for underground storage of rainwater or
stormwater runoff from parking lots, modular system is made from
100% recycled HDPE or polypropylene, large storage volumes
can be achieved.
Loomis Tank Center (ArroyoGrande, California; loomistank.com)
distributes and re-sells a wide range of tanks used in rainwater
harvesting systems. It offers fiberglass, HDPE, and galvanized
steel tanks from ten retail stores in the Southwest and through 40
manufacturing partnerships in 25 states.
Rain Harvesting Pty Ltd (Australian company, U.S. distribution
from Aurora, Illinois; rainharvesting.com): product developers, full
line of products, including filtering rain heads with debris filtration,
first-flush diverters, tank level monitors, tank overflow outlets, and
complete systems.
Rainwater Collection Solutions (Alpharetta, Georgia;
rainwaterpillow.com): Rainwater Pillow, an affordable, fabric
rainwater storage vessel made of a polyester scrim coated on
both sides with PVC, the pillows are flexible, resistant to freezing
20
down to –30°F, highly durable, available from 1,000 to 3,000
gallons, with custom offerings up to 200,000 gallons.
Rainwater HOG (Corte Madera, California; rainwaterhog.com):
modular rainwater storage tank for use in tight spaces like under
decks, against houses, or even within walls, made from foodgrade virgin polyethylene, each module holds 47.6 gallons. Tanks
can serve as thermal storage for passive solar heating systems.
Jay R. Smith (Montgomery, Alabama; jrsmith.com): systems and
components, seven pre-packaged systems, with the smallest
designed for roof areas up to 1,600 ft2 and the largest serving
roofs up to 5,500 ft2.
Snyder Industries (Lincoln, Nebraska; snydernet.com): Rain
Captor line, rotationally molded HDPE tanks for above-ground
(300–5,000 gallon) or below-ground (575–2,500 gallon)
installations.
Tank Town (Dripping Springs, Texas; rainwatercollection.com):
Tanks are either fiberglass (5,000- to 40,000-gallon capacity) or
lined steel (9,900- to 65,600-gallon capacity), Eliminator first-flush
storage tank that is designed to hold the first-flush rainwater that
may be too contaminated for potable use but is appropriate for
other uses, including compost tea. Produces its own line of
bottled water- licensed drinking water from harvested rainwater.
Wa t e r C o n t r o l C o r p o r a t i o n ( R a m s e y, M i n n e s o t a ;
watercontrolinc.com): storing water from a commercial building’s
drainage system and using that water for such non-potable
applications as landscape irrigation, toilet flushing, and cooling
tower and boiler make-up. Storage tanks can be polyethylene,
fiberglass, or lined galvanized steel up to 60,000 gallons in
capacity. Disinfection with ozone, UV, reverse osmosis, or
chemical treatment.
Water Filtration Company (Marietta, Ohio;
waterfiltrationcompany.com): filtration and treatment of surface
water sources such as ponds, lakes, and springs. Filtering
Roofwasher that installs between the downspout and the tank to
remove dirt and debris from water collected from a roof and
floating cistern filter, which reduces the final filtration loads.
Watertronics (Hartland, Wisconsin; watertronics.com) :
SkyHarvester line of custom-designed and -engineered systems
for commercial rooftop and parking-lot applications. Systems
designed for 3,000 gallons to 1 million gallons or more.
Xylem (White Plains, New York; completewatersystems.com) :
Flowtronex line of water pumps for landscape, rainwater, and
other low-head applications.
Yaktek Industries (www.yaktek.com.au, or U.S. distributor The
Rainwater Store; therainwaterstore.com): manufacturer of simple
tank level indicators, pulley-and-counterweight systems that show
the water level on the outside of the tank.
A watershed is a network of streams, creeks and ground water systems, which drain
rainfall and other freshwater from the land into the ocean, an estuary or a river. Every
square inch of land is a part of one watershed or another.
Whether you live on a farm, on the coast, in the woods or even in the desert, you live in a
watershed. Everyone lives in a watershed, as all lands drain rainfall to one body of water or
another. The watershed can be a source of sediment and pollution. As rainwater drains
from our yards, hillsides and streets it carries pollution with it. Think twice before you dump
cleaners, paint, oil and other chemicals on your yard, in the storm drain or in the street.
SLO Green Build
www.slogreenbuild.org
proudly partners with the following
municipalities. Please contact your
city or county building department for
questions, guidance and permitting.
Arroyo Grande
(805) 473-5426
www.arroyogrande.org
Atascadero
Public Works
(805) 461-5000
www.atascadero.org
Grover Beach
Community Development
Department
(805) 473-4520
www.grover.org
Morro Bay
City of Morro Bay - Public
Services
(805) 772-6261
www.morro-bay.ca.us
American Rainwater Catchment Systems
Association
www.arcsa-usa.org
Hardscapes: Patios and Driveways
GreenBuildingAdvisor.com
http://www.greenbuildingadvisor.com/
green-basics/hardscapes-patios-anddriveways-0
Harvesting, Storing, and Treating
Rainwater for Domestic Indoor Use
By Texas Commission on Environmental
Quality
http://rainwaterharvesting.tamu.edu/
drinking/gi-366_2021994.pdf
Harvesting Rainwater for Landscape Use
By University of Arizona Cooperative
Extension
http://cals.arizona.edu/pubs/water/
az1344.pdf
Natural Yard Care Guide
By Seattle Public Utilities
http://www.seattle.gov/util/Services/Yard/
Natural_Lawn_&_Garden_Care/
Natural_Yard_Care/index.asp
Rainwater Harvesting for Drylands and
Beyond
By Brad Landcaster
http://www.harvestingrainwater.com/
Rain Gardens: A How-to Manual for
Homeowners
By City of San Luis Obispo
http://clean-water.uwex.edu/pubs/pdf/
home.rgmanual.pdf
Rain Barrel Guide
http://www.rainbarrelguide.com/
Texas Manual on Rainwater Harvesting
By Texas Water Development Board
http://www.twdb.state.tx.us/publications/
reports/
RainwaterHarvestingManual_3rdedition.pdf
Slow it, Spread it. Sink it. A Homeowner’s
Guide to Greening Stormwater Runoff
By Resource Conservation District of
Santa Cruz County
http://www.rcdsantacruz.org/media/
brochures/pdf/
HomeDrainageGuide.v25.pdf
Paso Robles
(805) 237-3850
www.prcity.com
Pismo Beach
(805) 773-4656
www.pismobeach.org
City of San Luis Obispo
Community Development
Department
(805) 781-7530
(805) 781-7274
www.ci.san-luisobispo.ca.us
San Luis Obispo
County
Planning & Building
(805) 781-5600
www.sloplanning.org
Public Works
(805) 781-5252
Public Health
(805) 781-5500
City of Santa Barbara
Building & Safety
(805) 564-5485