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Water Quality Terms, Definitions and Web Resources

Action Level
The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow.

American Water Works Association (AWWA)
The American Water Works Association (AWWA) is an international nonprofit scientific and educational society dedicated to the improvement of drinking water quality and supply. Founded in 1881, AWWA is the largest organization of water supply professionals in the world. Its more than 50,000 members represent the full spectrum of the drinking water community: treatment plant operators and managers, scientists, environmentalists, manufactures, academicians, regulators, and others who hold genuine interest in water supply and public health. Membership includes more than 4,000 utilities that supply water to roughly 180 million people in North America.

Arizona Department of Environmental Quality (ADEQ)
The Arizona Department of Environmental Quality  functions as the local management and enforcement arm of the United States Environmental Protection Agency, and is responsible for ensuring the State of Arizona complies with all Federal water, air, and environmental regulations. Oro Valley Water Utility works with ADEQ to ensure the water we deliver meets all State and Federal standards for health and safety.

Arizona Department of Health Services (ADHS)
The Arizona Department of Health Services State Laboratory assists in protecting the health of Arizonans by providing a full range of Public Health Laboratory services, including identifying and investigating infectious and communicable diseases. The Laboratory monitors both groundwater and surface water for the presence of chemical and microbiological pollutants. The Department also maintains a laboratory licensure and consultation program that assures the quality of analytical testing being done by the clinical and environmental laboratory communities of Arizona.

Arizona Department of Water Resources (ADWR)
The Arizona Department of Water Resources works to secure long-term water supplies for Arizona’s communities. The Department administers state water laws (except those related to water quality), explores methods of augmenting water supplies to meet future demands, and develops policies that promote conservation and equitable distribution of water. Also, the Department oversees the use of surface and groundwater resources under state jurisdiction and negotiates with external political entities to protect Arizona’s Colorado River water supply. Other responsibilities include management of floodplains and non-federal dams to reduce loss of life and damage to property. ADWR is not a municipal water provider.

See Coliform Bacteria.

Chlorine is the most widely used drinking water disinfectant in North America. Adding a small amount of chlorine to drinking water protects the water from bacteria and other microorganisms. Chlorine is added to drinking water as either a gas or after having been already dissolved in water.

Chlorine is measured in the field using portable analytical instrumentation. The Utility works to maintain a chlorine level between 0.2 parts per million and 0.5 parts per million throughout the distribution system.

When the level of chlorine is above 0.5 parts per million, many people can smell chlorine in the water.

Coliform Bacteria
Coliforms are a type of bacteria which occur widely in the environment including surface water, soil, and decaying organic matter. This group of bacteria includes the fecal Coliform group which grows in the intestines of warm blooded animals. While this group of Coliform bacteria are generally not harmful in themselves, they have long been used as an indication of water quality.

Coliform samples are carefully collected in sterilized bottles at 58 sampling sites in the Utility’s distribution system. A certain portion of each sample is mixed with a nutrient medium and incubated for twenty-four hours. A color change or the production of gas indicates the presence of Coliform bacteria.

Corrosion occurs when metal is exposed to conditions which cause the breakdown of the metal through an exchange of ions. In water systems, this term generally refers to the rusting of metallic pipelines. Over time, corrosion will weaken the structure of the metallic pipes, resulting in leaks or breaks. Corrosion also can build up on the inside surface of the pipes, reducing water flow and contributing to water taste, odor, or color problems.

Distribution System
The Oro Valley Water Utility moves groundwater from wells to customer homes and businesses through an interconnected grid of water mains, valves, storage reservoirs, and pressure boosting or reducing facilities. This is generally referred to as the water distribution system.

Entry Point to the Distribution System (EPDS)
The point at which water is discharged into the distribution system from a well, storage tank, pressure tank, or water treatment plant.

Fluoride is a compound which occurs naturally in both groundwater and surface water. At low levels, fluoride can provide protection against tooth decay by increasing the durability of tooth enamel. The USEPA has set a maximum drinking water standard for fluoride of 4 parts per million (ppm). EPA has also set a secondary fluoride standard of 2 ppm to protect against dental fluorosis (tooth staining or pitting in developing teeth of children under 9 years old). In the drinking water delivered by the Utility, naturally occurring fluoride is found at levels between 0.1 to 0.6 ppm. The optimum fluoride level for drinking water is 0.8 ppm. Where the fluoride level of drinking water is less than 0.6 ppm, supplements may be worthwhile depending on the individual situation. Please see your medical provider. Currently, the Utility does not add fluoride to the drinking water supply.

Water Hardness
Many industrial and domestic water users are concerned about the hardness of their water. Hard water requires more soap and synthetic detergents for home laundry and washing, and contributes to scaling in boilers and industrial equipment. Hardness is caused by compounds of calcium and magnesium, and by a variety of other metals. Water is an excellent solvent and readily dissolves minerals it comes in contact with. Water hardness is generally divided into the following categories.

  • Soft 0 to 75 parts per million
  • Moderately Hard 75 to 150 parts per million
  • Hard 150 to 300 parts per million
  • Very Hard more than 300 parts per million

To convert hardness levels in parts per million to hardness in grains per gallon, divide by 17.1.

Water hardness in the Oro Valley area ranges from 30 ppm to 110 ppm. There is no governmental standard for water hardness. In fact, the National Research Council states that hard drinking water generally contributes a small amount toward total calcium and magnesium human dietary needs.

Less Than Symbol (< )
Values preceded with “<” indicate that the concentration of the substance being tested for was not detected at that level.

Maximum Residual Disinfectant Level (MRDL)
Maximum Residual Disinfectant Level (MRDL) means a level of a disinfectant added for water treatment that may not be exceeded without an unacceptable possibility of adverse health effects. The chlorine MRDL is set at 4 mg/L. A public water system is in compliance with the chlorine MRDL when the running annual average is less than or equal to the MRDL. MRDLs are enforceable in the same manner as the MCLs. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants. In certain instances, operators may increase the disinfectant levels of chlorine in the distribution system to a level and for a time necessary to protect public health to address microbiological contamination problems.

Microbiological Quality
Control of microorganisms in water served to customers may be the most important water quality protection that a water utility can perform. Microbiological quality in drinking water distribution systems is measured by the presence or absence of a type of bacteria called coliforms. State and Federal standards limit the number of positive total Coliform samples to no more than 5 percent of the total number of samples collected in the Utility’s distribution system. This is accomplished by adding a low level of disinfectant, usually chlorine, to the water distribution system and monitoring the water on an on-going basis. The Oro Valley Water Utility collects 58 samples every month from its distribution system to test for microbiological quality.

Mineral Content
Mineral content measures the amount of total dissolved solids, or TDS, in the water. The federal secondary drinking water standard for TDS is 500 parts per million. There are no health based limits for TDS in water.

90th Percentile Level
This is the value that is used to determine compliance with the action levels. If 90% of the samples are below the action levels (9 out of 10 samples), then the system is in compliance. In other words, no more than 10 percent of the samples may exceed the lead action level of 15 parts per billion. For copper, the action level is exceeded if more than 10 percent of the samples are above 1.3 parts per million. Also note that a 90th percentile result above the action level does not mean all customers are exposed to water above the action level. The number of samples collected is dependent on the population of the public water system.

Parts Per Billion (ppb)
Some constituents in water are measured in small units. Many of the trace metals such as mercury and organic compounds such as trihalomethanes monitored by the Utility are measured in terms of parts per billion (or micrograms per liter). To help you visualize how very small this unit is, we offer the following illustrations.

One part per billion equals:

  • 2 drops of water in a typical 15,000 gallon backyard swimming pool
  • One second of time in 31.7 years
  • The first 16 inches of a trip to the moon

Parts per Million (ppm)
Constituents in water are often measured in very small units. Many of the dissolved minerals such as sodium and calcium are monitored by the Utility are measured in terms of parts per million (or milligrams per liter). To help you visualize how very small this unit is, we offer the following illustrations.

One part per million equals:

  • ¼ cup of water in a typical 15,000 gallon backyard swimming pool
  • One second of time in eleven point six days.

Percentage of the samples or homes tested for a particular substance which fall above or below the action levels.

pH is a measurement of a water’s acidity. Waters with a pH below 7.0 are considered acidic, and are considered basic if pH is above 7.0. pH is measured in the laboratory or in the field, on the same day the water samples are collected from the system.

Potable and Non-Potable Water
Potable (pronounced “pote-able”) water is another term for drinking water. It refers to water which is safe to consume. The Utility’s potable water must meet very stringent State and Federal standards to be certified as safe for delivery to customers. Non-potable water is any water which does not meet those standards due to pollution, lack of proper treatment, or exposure to environmental contamination.

Public Water System
A public water system refers to a system that provides water for human consumption through pipes or other constructed conveyances, if such a system has at least 15 service connections or regularly serves an average of at least 25 individuals daily at least 60 days out of the year.

Sodium is a naturally occurring mineral which occurs in all drinking water in Oro Valley. While sodium is not regulated as a contaminant in drinking water, it may have an effect on the consumer’s health. In general, the sodium contributed to an individual’s diet from drinking water is a small part of overall dietary intake. The American Heart Association recommended standard for daily sodium intake is 3,000 milligrams. Persons on severely restricted sodium diets may want to consult their health professional regarding sodium levels in water.

The temperature of the water delivered by the Utility can vary depending on the time of year and the location where the measurement is taken. Part of the reason for this variability is that our water supply comes from more than 25 different wells, and groundwater temperature is a function of depth below the surface and the geology surrounding the well. The temperature of the water can also change as it flows through our drinking water system, depending on outside temperatures. The water at your tap can be 85 degrees or higher and can be affected by your private plumbing. Water temperature can affect the taste of your drinking water. Storing tap water in a clean container at room temperature or in the refrigerator will give a more refreshing taste.

Total Dissolved Solids (TDS)
See Mineral Content.

Trihalomethanes, or THMs, are produced when water is disinfected with chlorine and the chlorine reacts with naturally occurring organic matter found in all waters. Oro Valley groundwater contains very low levels of natural organic matter which accounts for the extremely low levels of THMs in the distribution system.

United States Environmental Protection Agency (USEPA)
The United States Environmental Protection Agency  is charged with protecting the environment and the health and safety of people by establishing standards for the use of many naturally-occurring and man-made compounds and resources. As a part of this effort, the agency is charged with regulating drinking water quality in the United States. They accomplish this through investigating the possible health effects of many naturally occurring and man-made compounds and regulating those which are shown to impact human health or the environment. For water systems, these regulations are developed as part of the Code of Federal Regulations under the Safe Drinking Water Act and its amendments. In Arizona, the Arizona Department of Environmental Quality functions as the local agency responsible for ensuring all water utilities comply with these regulations.