Water Quality Terms

Commonwealth of Virginia: Department of Health - Office of Water Programs (OWP)
The Department of Health - Office of Water Programs functions as the local management and enforcement arm of the United States Environmental Protection Agency, and is responsible for ensuring that the State of Virginia complies with all Federal water and and environmental regulations. The Water Authority works closely with OWP to ensure the water we deliver meets all State and Federal quality standards for health and safety.

Commonwealth of Virginia - Division of Consolidated Laboratory Services (DCLS)
The Commonwealth of Virginia Division of Consolidated Laboratory Services assists in protecting the health of Virginians by providing a full range of Public Health Laboratory services, including identifying and investigating infectious and communicable diseases. DCLS monitors and analyzes both groundwater and surface water for the presence of chemical and microbiological pollutants. The Division also maintains a laboratory licensure and consultation program that assures the quality of analytical testing being performed by the clinical and environmental laboratory communities of Virginia.

Chlorine
Chlorine is the most widely used drinking water disinfectant in North America. 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. Federal and Virginia regulations require at least 0.2 parts per million of chlorine where water enters the distribution system and at least a detectable amount of chlorine in 95 percent of the samples taken from the water distribution system. When the level of chlorine is above 0.5 parts per million, most people can smell chlorine in the water.

Cryptosporidium and Giardia
Cryptosporidium and Giardia are microorganisms that may be present in human and animal waste. Some people are more vulnerable to these contaminants in drinking water than the general population. Immuno-compromised individuals such as people undergoing chemotherapy, people who have received organ transplants, people who are HIV positive, people with AIDS, the young, and the elderly can be particularly at risk from these infections. Although these organisms have never been detected in water provided to its customers by the Western Virginia Water Authority, those persons with the preceding medical history or age characteristics should contact their personal health provider to be better informed as to the health risks associated with Cryptosporidium and Giardia. For additional information on Cryptosporidium and Giardia, please contact the Safe Drinking Water Hotline at 1-800-426-4791.

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 more than 60 sampling sites in the Water Authority water 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
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 Western Virginia Water Authority moves water treated at the Spring Hollow water treatment facility and 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.

Hardness
Hardness measures the ease with which soap can be lathered. It is easier to produce a lather using soft water. Water hardness is generally divided into the following categories.

Soft 0 to 75 parts per million
Moderate 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.

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 coliform. Under Federal and Virginia primary drinking water regulations, water utilities are required to keep the monthly average percentage of positive coliform samples below five percent. 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 Western Virginia Water Authority collects over 60 samples every month from its distribution system to test for microbiological quality. No positive bacteriological samples have been collected from the Water Authority's distribution system during the latest reporting period.

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 is no health basis for this level, but many people can detect a salty taste in the water when TDS is above 500 parts per million.

Parts Per Billion
Some constituents in water are measured in very small units. Many of the trace metals such as mercury and organic compounds such as trihalomethanes monitored by the RCUD 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:

One second of time in 31.7 years
The first 16 inches of a trip to the moon

Parts Per Million
Constituents in water are often measured in very small units. Many of the dissolved minerals such as sodium and calcium monitored by the RCUD 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:

1/4 ounce of water in a typical 15,000 gallon backyard swimming pool
One second of time in eleven point six days

pH
pH is a measurement of a water's acidity. Waters with a pH below 7.0 are considered acidic, those with a pH above 7.0 are considered basic. pH is measured in the laboratory 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. Water Authority 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.

Sodium
Sodium is a naturally occurring mineral which occurs in all drinking water in the Roanoke Valley. While sodium is not regulated as a contaminant in drinking water, it may have an effect on the consumer's health. Generally, the amount of sodium contributed to an individual's diet from drinking water is a small part of overall dietary intake. The American Heart Association's 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.

Statistical Terms
Coefficient of Variation is a measure of the relative variation around the mean. Calculated by dividing the standard derivation by the mean.
Count is the number of data values in a data set.

Maximum is the highest value of a group of numbers. The listing of the minimum and maximum values describes the range of a data set.

Mean is the average value of a group of data calculated by summing up the values and dividing by the number of data points (the count).

Median is the mid point of a set of data points. 50 percent of the values will be above the median value and 50 percent will be below the median value.

Minimum is the lowest value of a group of numbers.

Standard Deviation is a measure of the variation around the mean of a group of numbers.

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

The federal primary drinking water standard for THMs is 100 parts per billion (PPB). The maximum total THM level measured in the Water Authority distribution system is 24 PPB.

United States Environmental Protection Agency (US EPA)
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 Virginia, the Department of Health - Division of Water Programs functions as the local agency responsible for ensuring all water utilities comply with these regulations.

Water Quality Zone
A Water Quality Zone is an area of the water distribution system based on water pressure levels, as well as, geographical and political boundaries.