Testing Water Quality:
What to Test and Why
Temperature
Information from iub.edu
The water temperature of a river is very important for water quality. Many of the physical,
biological, and chemical characteristics of a river are directly affected by temperature. For
example, temperature influences:
1.
2.
3.
4.
the amount of oxygen that can be dissolved in water;
the rate of photosynthesis by algae and larger aquatic plants;
the metabolic rates of aquatic organisms;
the sensitivity of organisms to toxic wastes, parasites, and diseases.
Remember, cool water can hold more oxygen than warm water, because gases are more easily
dissolved in cool water.
Human-Caused Changes in Temperature
One of the most serious ways that humans change the temperature of rivers and lakes is through
thermal pollution. Thermal pollution is an increase in water temperature caused by adding relatively
warm water to a body of water. Industries, such as nuclear power plants, may cause thermal pollution
by discharging water used to cool machinery. Thermal pollution may also come from stormwater
running off warmed urban surfaces, such as streets, sidewalks, and parking lots.
Changes in Aquatic Life
As water temperature rises, the rate of photosynthesis and plant growth also increases. More plants
grow and die. As plants die, they are decomposed by bacteria that consume oxygen. Therefore, when
the rate of photosynthesis is increased, the need for oxygen in the water (BOD) is also increased.
Most aquatic organisms have adapted to survive within a range of water temperatures, Some organisms
prefer cooler water, such as trout, stonefly nymphs, while others thrive under warmer conditions, such
as carp and dragonfly nymphs. As the temperature of a river increases, cool water species will be
replaced by warm water organisms. Few organisms can tolerate extremes of heat or cold.
Temperature also affects aquatic life's sensitivity to toxic wastes, parasites, and disease. For example,
thermal pollution may cause fish to become more vulnerable to disease, either due to the stress of rising
water temperatures or the resulting decrease in dissolved oxygen.
Dissolved Oxygen
Information from USGA Water Quality Monitoring
Dissolved Oxygen (DO) is found in microscopic bubbles of oxygen that are mixed in the water and
occur between water molecules. DO is a very important indicator of a water body's ability to support
aquatic life. Fish "breathe" by absorbing dissolved oxygen through their gills. Oxygen enters the water
by absorption directly from the atmosphere or by aquatic plant and algae photosynthesis. Oxygen is
removed from the water by respiration and decomposition of organic matter.
Factors Affecting DO

Volume and velocity of water flowing in the water body
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Climate/Season
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The type and number of organisms in the water body
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Altitude
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Dissolved or suspended solids
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Amount of nutrients in the water
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Organic Wastes
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Riparian Vegetation
Biochemical Oxygen Demand (BOD)
Information from epa.gov
The stream system both produces and consumes oxygen. It gains oxygen from the atmosphere and from
plants as a result of photosynthesis. Running water, because of its churning, dissolves more oxygen than
still water, such as that in a reservoir behind a dam. Respiration by aquatic animals, decomposition, and
various chemical reactions consume oxygen.
Wastewater from sewage treatment plants often contains organic materials that are decomposed by
microorganisms, which use oxygen in the process. The amount of oxygen consumed by these organisms
in breaking down the waste is known as the biochemical oxygen demand or BOD. Other sources of oxygenconsuming waste include stormwater runoff from farmland or urban streets, feedlots, and failing septic
systems.
BOD Values for the Libby River, Me.
Turbidity
Information from epa.gov
Turbidity is a principal physical characteristic of water and is an expression of the optical
property that causes light to be scattered and absorbed by particles and molecules rather
than transmitted in straight lines through a water sample. It is caused by suspended matter
or impurities that interfere with the clarity of the water. These impurities may include
clay, silt, finely divided inorganic and organic matter, soluble colored organic compounds,
and plankton and other microscopic organisms. Typical sources of turbidity in drinking
water include the following:
Waste discharges;
Runoff from watersheds, especially those that are disturbed or eroding;
Algae or aquatic weeds and products of their breakdown in water reservoirs,
rivers, or lakes;
Humic acids and other organic compounds resulting from decay of plants,
leaves, etc. in water sources; and
High iron concentrations which give waters a rust-red coloration (mainly in
ground water and ground water under the direct influence of surface water).
Air bubbles and particles from the treatment process (e.g., hydroxides, lime
softening)
Simply stated, turbidity is the measure of relative clarity of a liquid. Clarity is important
when producing drinking water for human consumption and in many manufacturing uses.
Once considered as a mostly aesthetic characteristic of drinking water, significant evidence
exists that controlling turbidity is a competent safeguard against pathogens in drinking
water.
Phosphates
Information from LaMotte Manual
Phosphorus is an important nutrient for aquatic plants. The amount found in water is generally not
more than 0.1 ppm unless the water has become polluted from waste water sources or excessive
drainage from agricultural areas. When phosphorus is present in excess of the concentrations required
for normal aquatic plant growth, a process called eutrophication takes place. This creates a favorable
environment for the increase in algae and weed nuisances that produce scums and odors. When algae
cells die, oxygen is used in the decomposition and fish kills often result. Rapid decomposition of dense
algae scums with associated organisms give rise to foul odors and hydrogen sulfide gas. Inorganic
phosphate, which is largely the form of phosphorus required for plant growth, is determined by its
reaction with a molybdate solution to form a phosphomolybdate which, when reduced, forms a blue
color which is the basis for a very sensitive test for phosphorus. The production of more than a faint
blue color in this test is cause for suspicion of phosphate pollution, and when the other factors such as
available nitrogen, iron, trace metals, etc. are present, will cause the conditions described above.
Nitrates
Information from LaMotte Manual
Nitrogen is essential for plant growth but the presence of excessive amounts in water supplies presents
a major pollution problem. Nitrogen compounds that may enter water as nitrates, or be converted to
nitrates, can originate from agricultural fertilizers, sewage, industrial and packing house wastes,
drainage from livestock feeding areas, farm manures and legumes. Nitrates in large amounts can cause
birth defects in livestock production. Nitrates, in conjunction with phosphates, stimulate the growth of
algae with all of the related difficulties associated with excessive algae growth.
US Public Health Service Drinking Water Standards state that 10 ppm Nitrate Nitrogen is a limit which
should not be exceeded. However, to the sanitary and industrial engineer, the concentration which is of
concern is less than 1 ppm.
In the chemical test for nitrates, a red dye is formed by the coupling of two chemical intermediates
through the action of nitrates derived from the reduction of the nitrate ion.33
The Nitrogen Cycle
Nitrate Levels of Monterey Bay
pH
Information from LaMotte Manual
Most natural waters will have pH values from pH 5.0-8.5. Acidic, freshly fallen rain water may have a
pH value of pH 5.5-6.0. If it reacts with soils and minerals containing weak alkaline materials, the
hydroxyl ions will increase and the hydrogen ions decrease; the water may become slightly alkaline
with a pH of pH 8.0-8.5. Sea water will have a pH value close to pH 8.0.
Waters more acidic than pH 5.0 and more alkaline than pH 8.5-9.0 should be viewed with suspicion.
Mine drainage and acid industrial wastes are the principal factors in increasing the acidity of water, and
alkaline industrial wastes are the cause of high pH values.
The pH test, which is one of the most important tests for detecting industrial pollution, is also one of
the simplest to perform. *Range Finding Indicator Solution (2220) contains several indicators. A
specific color forms at each pH as a result of the reaction between the water sample and the indicators.
pH Scale
pH Effects on Aquatic Life
11.0-11.5
10.5-11.0
9.0-10.5
8.2-9.0
water
6.5-8.2
6.0-6.5
5.5-6.0
5.0-5.5
4.5-5.0
4.0-4.5
3.5-4.0
3.0-3.5
Rapidly lethal to all species of fish
Rapidly lethal to salmonids. Prolonged exposure is lethal to carp, perch
Likely to be harmful to salmonids & perch if present for long periods
Unlikely to be directly harmful to fish, but indirect effects due to chemical changes in
Optimal for most organisms
Freshwater shrimp absent. Unlikely to harm fish unless free carbon dioxide in above
100 ppm
Metals (Aluminum, Lead) normally trapped in sediments are released into water in toxic
form to fish
Bottom dwelling bacteria begin to die. Leaf litter and detritus begin to accumulate
locking up essential nutrients and interrupting chemical cycling. Plankton begin to
dissapear. Snails and clams absent.
Mayfly and many other insects absent. Most fish eggs will not hatch.
All fish, most frogs, insects absent
Known to be lethal to salmonids
Unlikely that fish can survive more than a few hours in this range although some plants
and invertebartes can be found at pH levels this low.
Water Testing: Overview
Information from the LaMotte Manual
Temperature
Temperature is very important to water quality. Temperature affects the amount of dissolved oxygen
in the water as well as the rate of photosynthesis of aquatic plants. Thermal pollution, the discharge of
heated water, can cause temperature changes that threaten the balance of aquatic systems.
Dissolved Oxygen
All aquatic animals need oxygen to survive. Natural waters with consistently high dissolved oxygen
levels are most likely healthy and are capable of supporting a diverse aquatic environment. Cold water
holds a greater amount of dissolved oxygen than warm. High levels of bacteria from sewage pollution
or large amounts of rotting plants can cause dissolved oxygen to decrease.
Biochemical Oxygen Demand (BOD)
Biochemical oxygen demand is a measure of the quantity of dissolved oxygen used by bacteria as they
break down organic wastes. In slow moving or polluted rivers, much of the available dissolved oxygen
is consumed by bacteria, robbing other aquatic organisms of the oxygen needed to live.
Turbidity
Turbidity is the measure of the relative clarity of water. Turbid water is the result of suspended matter
such as clay, silt, and organic material. Turbidity should not be confused with color since darkly
colored water can still be clear and not turbid. Turbid water may be the result of soil erosion, urban
runoff, algal blooms, and, bottom sediment disturbances.
Phosphates
Phosphorus is needed by all organisms, but when phosphorus is present in excess in water
environments, a process called eutrophication takes place. Eutrophication is increased algae and weed
growth that produces scums and odors. When the algae cells die, oxygen is used in the decomposition
and fish kills often result. High phosphate levels are often from excessive use of fertilizers.
Nitrates
Nitrogen is essential for plant growth but the presence of excessive amounts in water supplies presents
a major pollution problem. Nitrogen compounds that may enter water as nitrates and can originate
from agricultural fertilizers, sewage, or industrial or agricultural wastes. Nitrates, in conjunction with
phosphates, can stimulate excessive algae growth.
pH
pH is a measure of hydrogen ions in solution (pH stands for potential hydrogen) and is a scale from 0
to 14. Most natural waters will have pH values from pH 5.0-8.5. Acidic, freshly fallen rain water may
have a pH value of pH 5.5-6.0 (commonly referred to as acid rain due to pollution). If it reacts with
soils containing weak alkaline materials, hydroxyl ions will increase and the hydrogen ions decrease;
the water may become slightly alkaline with a pH of 8.0-8.5. Sea water will have a pH value close to
8.0. Waters more acidic than pH5.0 and more alkaline than pH8.5-9.0 should be viewed with
suspicion. Mine drainage and acid industrial wastes are the principal causes of low pH values, and
alkaline industrial wastes are causes of high pH values.
Coliform Bacteria
Fecal coliform are naturally present in the human digestive tract, but are rare in unpolluted waters.
The presence of coliform bacteria is a reliable indication of sewage in a waterway. Coliform bacteria
can be dangerous to human health. This test indicates total and all coliform bacteria strains present.