Embodied Energy of Lost Water: Evaluating the Energy Efficiency of Infrastructure
Investments
Craig Aubuchon, Analysis Group, Inc.
111 Huntington Avenue, 10th Floor
Boston, MA 02199
(617) 425-8000
J. Alan Roberson, American Water Works Association
West 1300 Eye Street NW
Washington, DC 20005
(202) 628-8303
ABSTRACT
In recent years, the water and wastewater industries have seen an increased interest in research,
funding, and application of energy efficiency investments related to the production and
distribution of clean water. However, during this same period, funding needs for traditional
distribution and infrastructure issues have also continued to increase. Since a primary concern
with infrastructure investments is to reduce the amount of non-revenue or lost water, the current
research combines data from three novel sources to estimate the embodied energy of nonrevenue water. We find that the mean embodied energy of lost water for 270 utilities in 2010 was
1,849 MWh of electricity and 1,360 short tons of CO2. These findings compare favorably to
other energy efficiency programs implemented for water and wastewater treatment plants under
the 2009 American Recovery and Reinvestment Act. Therefore, the magnitude of these findings
suggests that for some utilities, investment in infrastructure replacement may provide significant
energy efficiency benefits.
KEYWORDS
Non-Revenue Water; Embodied Energy; Carbon Emissions
INTRODUCTION
The Environmental Protection Agency (“EPA”) estimates that drinking water and wastewater
systems account for almost 4% of total U.S. energy use. 1 In part to address the significance and
magnitude of this number, the 2009 American Recovery and Re-investment Act (“ARRA”)
initiated several new investments in energy efficiency projects for water and wastewater
utilities.2 These investments came at a critical time and demonstrated a renewed interest in water
utility infrastructure, particularly as it relates to energy use . However, as the groundbreaking
AWWA report, ‘Buried No Longer’ highlighted, the necessary investments to replace
underground infrastructure could approach over $1 trillion over the next 25 years. 3 This fact
alone explains why ‘infrastructure’ is consistently identified as one of the top industry concerns
over the next five years (Murphy, 2011).
However, the same State of the Industry Report also identified ‘infrastructure’ as the most
inadequately addressed issue. To help address the current gap between funding available for
energy efficiency energy projects and the growing financial needs for underground infrastructure
investment, this analysis estimates the embodied energy non-revenue/lost water for a subset of
utilities from the 2010 American Water Works Association/Raftelis Financial Consulting
(AWWA/RFC) rates survey. In particular, we find that by combining simple engineering
estimates of unit electricity consumption with regional emissions rates, the mean embodied
energy of lost water for 270 utilities in 2010 was 1,849 MWh of electricity and 1,360 short tons
of CO2. The magnitude of these findings suggests that for some utilities, investment in
infrastructure replacement may provide significant energy efficiency benefits.
Where does Efficiency fit into the Water-Energy Nexus?
Two statistics are often used in the context of a discussion of the water-energy nexus; the first
has already been mentioned: EPA estimates that drinking water and wastewater systems account
for approximately 4% of total U.S. energy use. The second refers to water consumption by
energy utilities: thermoelectric power generation water withdrawals account for roughly 50% of
total U.S. withdrawals (USGS, 2009). Others have offered refinements on these general
estimates, but the end goal is the same – to estimate the resource consumption of one sector from
another sector. 4
Typical energy efficiency investments in the water sector have focused on efforts to reduce
energy use for water treatment and distribution. These include strategies to optimize pumping
systems, treatment systems and to generate energy resources on-site (EPA, 2008, 2010; ACEEE,
2013). These investments are an important strategy to reduce overall energy use and lower
carbon emissions since they target one of the largest sectors of electricity nation-wide. The point
of the present research is not to suggest that energy efficiency investments are poor allocations of
public funds or revenue; rather, the question is how to best maximize scarce resources among
often times competing and important priorities. Thus, consideration of the water-energy nexus
helps to show that reductions in water demand can also reduce energy consumption, since less
raw water must be treated, regardless of the pump efficiency. Equally important, reductions in
water demand at the distribution/retail stage also benefit electricity generation units to the extent
that there is less demand on raw water sources.
Non-revenue water, defined as the difference between the water that leaves the treatment plant
and the water that is metered at the customer tap requires energy to produce and at the same
time, represents raw water that is not available to other uses such as power generation. As the
name suggests, it costs the utility money to produce the water, but because the water is lost
during distribution, it is not available to generate revenue. Thus, non-revenue water represents an
important win-win-win opportunity by reducing energy use through an optimization of treatment
volumes, increasing raw water supplies for other uses, and increasing revenues (or decreasing
production costs) for water utilities. By presenting the energy-efficiency benefits from
investments in distribution infrastructure, it may be possible to align funding needs more closely
with spending priorities.
The growing gap between funding priorities and needs is illustrated by the 2007 Drinking Water
Infrastructure Needs Survey and Assessment (DWSRF, 2009), which estimated that
infrastructure spending needs for the 2007-2026 period was $334.8 billion, with 60% of that
need for transmission and distribution and 22% for treatment. In contrast, during the 2009
program cycle, the Drinking Water State Revolving Fund (“DWSRF”) allocated 37% of
assistance to transmission and distribution and 43% to treatment needs. The 2009 DWSRF
annual report notes that funding for treatment projects better meet the public health protection
objective of the DWSRF, while distribution projects are more often financed by cash reserves or
on a pay-as-you-go basis. However, the 2009 ARRA funding demonstrated a higher level
concern with energy efficiency: the Department of Energy received $28.5 billion in awards for
contracts/grants/loans, while the EPA and the Clean Water and Safe Drinking Water Revolving
Funds received $4 and $2 billion, respectively.
METHODOLOGY
To calculate the embodied energy in lost water, we combine several data sources in a novel
manner. In particular, we use:
•
•
•
The 2010 AWWA/RFC rates survey, which sampled over 300 water and wastewater
utilities. This survey includes data on Utility size, region, rates, capacity, demand, and
lost water.
Unit Energy Consumption estimates from the 2002 Electric Power Research Institute
(EPRI) report that underlies the 4% energy consumption number routinely cited from the
EPA.
CO2 emissions rate models from the EPA Emissions & Generation Resource Integrated
Database (eGRID) for the year 2009 power generation sector.
The 2010 AWWA/RFC rate survey is among the largest and most detailed rate surveys of its
kind. Figure 1 shows the distribution of surveyed utilities across the U.S. An important caveat to
using the AWWA/RFC data is that the survey is not a random sample of utilities; in particular, it
is known to oversample larger utilities, particularly in the west and southwest. Therefore, it is
important to consider that the average energy use values or average carbon emissions presented
here may not be representative of a true national average. Instead, what is important is the
general magnitude of the findings and the method by which individual utilities can easily
replicate these results using their own utility specific data in a benefit cost analysis test for future
infrastructure projects. The rate survey classifies utilities into three groups (group A utilities have
average daily sales greater than 75 MGD; group B utilities serve greater than 20 MGD per day,
and group C utilities serve less than 20 MGD) and four regions (Northeast, South, West,
Midwest). Within the survey, not all utilities reported values for daily treatment capacity, lost
water as a percentage of total sales, and annual rates. After dropping utilities without relevant
data, we were able to estimate the embodied energy of 270 utilities; 39 group A utilities, 78
group B, and 153 group C utilities. Of these 270, 82 were located in the West, 112 in the South,
52 in the Midwest, and 24 in the Northeast.
Figure 1. Water and Wastewater Utilities in the 2010 American Water Works Association/
Raftelis Financial Consulting Survey
For each utility, the embodied energy of lost water was calculated as:
Equation 1. 𝐸𝑚𝑏𝑜𝑑𝑖𝑒𝑑 𝐸𝑛𝑒𝑟𝑔𝑦 (𝑀𝑊ℎ) 𝑜𝑓 𝐿𝑜𝑠𝑡 𝑊𝑎𝑡𝑒𝑟 = 𝑇𝑜𝑡𝑎𝑙 𝐺𝑎𝑙𝑙𝑜𝑛𝑠 𝑆𝑜𝑙𝑑 (𝑀𝑀𝐺𝑎𝑙) ∗
𝑘𝑊ℎ
1𝑀𝑊ℎ
𝐿𝑜𝑠𝑡 𝑊𝑎𝑡𝑒𝑟 (%) ∗ 𝑈𝑛𝑖𝑡 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦 𝐶𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 �𝑀𝑔𝑎𝑙� ∗ (1000𝑘𝑊ℎ)
Table 1 provides the EPRI (2002) estimates for the total unit electricity consumption by
treatment plant size and source water.
Table 1: Total Unit Electricity Consumption by Plant Size
Treatment Plant Size
Unit Electricity Consumption
(MGD)
(kWh/Mgal)
1
5
10
20
50
100
1,483
1,418
1,406
1,409
1,408
1,407
Note: GW is 30% higher, independent of the size of pump
From the AWWA/RFC data, we were able to estimate unit electricity consumption for each
utility based on its source water and size. First, the utility was matched to the EPRI data based on
its daily treatment capacity (for example, a utility with a daily treatment capacity of 17 Mgal was
assumed to have a unit electricity consumption of 1,409 kWh/Mgal). Second, we calculated the
weighted average of electricity consumption from the proportion of source water from surface
and ground water, with ground water requiring 30% higher energy consumption. We assumed
that all wholesale purchases of water came from surface water plants; this is a conservative
estimate for the embodied energy consumption, particularly since it doesn’t account for the
energy required for transmission between wholesale provider and the distribution utility.
Table 2 provides descriptive statistics for the lost water (in pct and Mgal) and embodied
electricity consumption for the utilities in our sample. 5 The AWWA/RFC survey includes the
question:
“Please provide the estimated percentage of water loss for your utility in your 2009 operating
period”
Unfortunately, this question does not differentiate between lost water and non-revenue water.
AWWA (1996) defines ‘lost water’ as: unidentified leakage, meter inaccuracies, theft, underestimated accounts, improperly typed and sized meters, meter reading errors, and accounting
errors. It is unclear how utilities interpreted this question; in contrast to non-revenue water, lost
water could include known leaks and losses. The water loss percentage reported on the survey
form could either overstate non-revenue water, if it includes known leaks, or it could understate
non-revenue water if it does not fully account for unknown losses. In the present analysis, we do
not differentiate among the reasons for lost water. Although our focus is on recapturing lost
water due to leakage, increases in meter accuracy and accounting errors could also reduce
demand, particularly if they require the customer to pay for water they had previously been
unbilled.
Most utilities self-reported lost water values less than 10%, the recommended measure from
AWWA (1996). However, the utilities with the greatest water loss all reported values greater
than 20%, irrespective of size or region. Within the current panel, water loss is highest, both in
maximum percentages and in mean loss, for the Northeast and Midwest. In both regions, nearly
60% of the current infrastructure was built prior to 1940 (AWWA, 2012) and contains a high
percentage of cast iron pipes. The same is true for the total amount of water lost (in Mgal).
In contrast, the Northeast has the lowest unit electricity cost, possibly reflecting a higher
proportion of surface water systems in the sample. The mean unit electric rate is 1,480
kWh/Mgal in the Northeast, 1,577 in the Midwest, 1,522 in the South and 1,530 in the West. In
terms of gross embodied energy, the Northeast still has the highest average, while larger systems
(with a larger volume of total water lost) also have higher rates of lost embodied energy.
Table 2: Reported Values for Lost Water (% and Mgal/year) and Estimated Unit Energy Consumption of Lost Water
Lost Water (pct)
Utility Sub-Sample
Total
A
B
C
West
South
Midwest
Northeast
Min
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.03
Max
0.38
0.38
0.38
0.32
0.23
0.31
0.38
0.38
Mean
0.11
0.11
0.10
0.11
0.08
0.11
0.13
0.17
Median
0.09
0.10
0.08
0.09
0.07
0.10
0.12
0.16
Std
0.07
0.08
0.07
0.07
0.05
0.06
0.08
0.09
Count
275
41
79
155
84
114
53
24
Lost Water (Mgal)
Total
A
B
C
West
South
Midwest
Northeast
0.11
613
86
0.11
0.11
14.28
23.11
65.42
35,837
35,837
5,181
7,923
6,768
25,316
19,357
35,837
1,591
6,576
1,317
452
1,040
1,516
1,487
4,027
522
4,977
1,071
274
455
523
435
1,628
3,474
7,052
955
824
1,473
2,883
3,174
7,957
269
39
78
152
81
112
52
24
Embodied Energy
Consumption of
Lost Water (MWh)
Total
A
B
C
West
South
Midwest
Northeast
0.18
863
134
0.2
0.18
20
42
94
50,423
50,423
7,290
11,147
13,048
38,826
27,235
50,423
2,369
9,762
1,955
685
1,586
2,288
2,231
5,695
787
7,468
1,561
423
703
791
613
2,292
5,059
10,175
1,353
1,178
2,304
4,439
4,547
11,185
269
39
78
152
81
112
52
24
Next, we use emissions rate data from the EPA eGRID database 6 to calculate the embedded CO2
emissions in lost water as a function of the embodied energy used during production. Carbon
emission rates vary regionally based on the electricity generating units within each power region.
The eGRID database calculates the average annual emission rate based on 2009 power plant data
for actual CO2 emissions and generation rates. Regions with more coal units have higher
emission rates, while regions with more natural gas or hydropower generation units have lower
CO2 rates. Aggregated up from the EPA subregions to the AWWA/RFC regions, the mean
emission rate for energy consumed by water utilities was 817 lbs CO2 per MWh for the
Northeast, 934 lbs CO2/MWh in the West, 1200 lbs CO2/MWh in the South, and 1617 lbs
CO2/MWh in the Midwest. Figure 3, taken from the EPA eGRID database, shows the 22 subregions of the North American Electric Reliability Corporation (NERC).
Figure 2.EPA eGRID sub-region representational map
The current version of the eGRID power profiler zip code tool allows data users to input up to
2000 zip codes, and it then automatically determines the eGRID sub-region and displays total
output emission rates for CO2, N20, and CH4. Previous iterations of the eGRID database have
also provided data for non-base load emission rates. The total CO2 emissions embodied was
determined as:
Equation 2.
𝐸𝑚𝑏𝑜𝑑𝑖𝑒𝑑 𝐸𝑚𝑖𝑠𝑠𝑖𝑜𝑛𝑠 (𝑠ℎ𝑜𝑟𝑡 𝑡𝑜𝑛𝑠 𝐶𝑂2) 𝑜𝑓 𝐿𝑜𝑠𝑡 𝑊𝑎𝑡𝑒𝑟 =
𝑙𝑏𝑠 𝐶𝑂2
𝐸𝑚𝑏𝑜𝑑𝑖𝑒𝑑 𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝐿𝑜𝑠𝑡 𝑊𝑎𝑡𝑒𝑟 (𝑀𝑊ℎ) ∗ 𝑒𝐺𝑅𝐼𝐷 𝑇𝑜𝑡𝑎𝑙 𝐸𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟 ( 𝑀𝑊ℎ )
RESULTS
We were able to calculate embodied CO2 emissions for 270 utilities in the AWWA/RFC rate
survey. The wide range of values depends on three main factors: the volume of lost water, the
amount of energy required to treat and produce the water, and the underlying generation
technology to produce the electricity. Table 3 provides additional details on the embedded CO2
emissions. Values range from a low of 0.06 short tons of CO2 in the 2009 year for a small utility
in the West to a high of 22,941 short tons of CO2 for a large utility in the South. The average
embodied emissions for the full sample is 1,333 short tons of CO2, but due primarily to the
volume of lost water, larger systems tend to have higher total embodied CO2 emissions. Utilities
in the Northeast have the highest mean level of embodied CO2 at 2,094 short tons of CO2, while
the West has almost a third as much, at 780 short tons of CO2 for the average utility.
Table 3: Estimated Embodied CO2 Emissions in Lost Water
Utility SubSample
Min
Max
Mean
Total
0.06
22,941
1,333
A
788
22,941
5,601
B
80
3,053
1,039
Embodied
C
0.06
5,281
395
Emissions
(Short tons West
0.06
10,395
780
CO2)
South
12
22,941
1,376
Midwest
32
20,706
1,764
Northeast
34
15,396
2,094
Median
452
4,413
917
218
264
468
501
814
Std
2,707
5,192
681
623
1,403
2,652
3,493
3,953
Count
270
39
78
153
82
112
52
24
SUMMARY AND CONCLUSIONS
These findings compare favorably to other energy efficiency programs implemented for water
and wastewater treatment plants. For example, in 2007, the Massachusetts Department of
Environmental Protection (MassDEP) initiated a pilot program to reduce greenhouse gas
emissions and energy use at water treatment facilities by 20%. This program later received
significant funding under the 2009 ARRA and highlighted as an EPA pilot project. 7 The project
included 14 utilities (7 each from the water and wastewater sectors) and included a wide variety
of size and technologies. The program included a wide range of stakeholders, including
academic institutions, energy efficiency non-profits, regional government divisions, and major
electric and gas providers, who offered energy audits to the water participants. The MassDEP
estimates that these green investments, at a total of 21 completed project sites, will ultimately
save 22,000 tons of CO2 and 29 million kWh of electricity. Within this total, the majority of
water and wastewater plants identified annual CO2 reductions of approximately 400 tons. The
largest exceptions were for wastewater treatment plants that identified Digester and HVAC
improvements, resulting in large decreases in natural gas usage and a larger GHG reduction. 8
Indeed, for just the Northeast region alone, the estimated embodied CO2 emissions in lost water
was slightly more than 50,000 tons of CO2 and 136 million kWh. This suggests that lost water
may be a critically important area for energy efficiency measures.
The 2009 American Recovery and Reinvestment Act provided much needed funding to the
Clean Water and Safe Drinking Water State Revolving Funds. The majority of this money was
spent on traditional projects, while 29% was allocated to Green Project Funding in terms of both
water efficiency and energy efficiency. However, as this research demonstrates, investments in
water efficiency, and even more narrowly, investments in distribution infrastructure, are not
exclusive from energy efficiency investments. The estimates presented here suggest that the
embodied energy of lost water is comparable to, and in many instances greater than, the reported
energy efficiency savings from other ARRA EE investments in the water sector. The mean
embodied energy of lost water in the AWWA/RFC sample was 2,300 kWh and 1,333 tons of
CO2, with findings varying significantly by region and utility size. This research presents an
important first step in addressing the stated need for infrastructure funding and the actual
allocation of investment dollars. Future research should consider how water utilities can apply
and present generalized versions of rate payer funded energy efficiency cost-effectiveness tests
to their more traditional resource and infrastructure spending needs. Under these costeffectiveness tests, utilities should consider the non-resource values embedded in electricity costs
and external social pollution, such as carbon dioxide. By presenting these benefits to other
stakeholders, including energy providers, state regulators, and energy-efficiency non-profits, the
water utility sector can broaden its base of supporters for infrastructure funding and continue to
address the significant infrastructure challenges on the horizon.
.................................
1
For example, see: http://water.epa.gov/infrastructure/sustain/energyefficiency.cfm. This 4% number appears to be
based on the initial work presented in EPRI (2002) and accounts for the production, conveyance, and treatment
of water and wastewater. More broadly, estimates indicate that energy for water services such as end-use heating
may be as high as 12% of total U.S. energy use (Sanders and Webber, 2012).
2
For example, see: http://water.epa.gov/infrastructure/sustain/energyefficiency.cfm and
http://www.mass.gov/dep/water/priorities/eerewwu.htm.
3
http://www.awwa.org/portals/0/files/legreg/documents/buriednolonger.pdf
4
For example, Macknick et al. (2011) have refined the USGS estimate of water needs by the power sector and
developed technology specific estimates of water withdrawal and consumption rates by generation technology.
5
We have excluded utilities that reported zero lost water or zero annual total sales.
6
The EPA eGRID database is available for public download at: http://www.epa.gov/cleanenergy/energyresources/egrid/index.html
The 2012 release presents emissions rate data from 2009 power plant reported values. The power profiler tool
calculates the average CO2 emissions at a zip code level.
7
See:
http://water.epa.gov/aboutow/eparecovery/upload/2010_01_26_eparecovery_ARRA_Mass_EnergyCasyStudy_lowres_10-28-09.pdf
8
The primary constituent of natural gas is methane (CH4), which is 21 to 25x more potent than CO2 as a GHG over
a 100 year time period (IPCC, 2007). Totals by facility: the Barnstable Wastewater Treatment Facility (1,931 tons
of CO2), Falmouth Wastewater Treatment Facility (3,200 tons of CO2), Greater Lawrence Sanitary District (5,887
tons of CO2), and Pittsfield Wastewater Treatment Facility (3,252 tons of CO2). See:
http://www.mass.gov/dep/water/priorities/empilot.htm for specific details of plant programs.
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