Tap Water Sources
Our water supply comes from either a surface water or groundwater source. These sources are found within a watershed, which are those land areas that are bounded by ridge lines that catch rain and snow, and drain to specific marshes, streams, rivers, lakes, or to groundwater(5). Watersheds are important because activities within them affect water quality(5). You can gain valuable information about watersheds from the Environmental Protection Agency (EPA) Office of Wetlands, Oceans, and Watersheds. You can obtain information and look at a map of your watershed at the EPA's Index of Watershed Indicators. The EPA also has an "Adopt Your Watershed" program. Through this program, you can join the EPA in protecting and restoring the nations valuable surface and groundwater sources. If you would like to get involved with other issues pertaining to water, you can find more information from the EPA Office of Water Citizen's Guide.
One of the best resources for learning more about drinking water, how it is protected, legislation, publications, newsletters, and programs is the EPA Office of Ground Water and Drinking Water. Perhaps the most extensive database available on drinking water information is the EPA Safe Drinking Water Information System (SDWIS). This database allows you to locate your drinking water supplier and view violation and enforcement history for the last ten years. You can also take a look at the quality of water in your state, according to the EPA.
Approximately 1/2 of drinking water in the U.S. comes from groundwater sources (2). Groundwater is drawn from subsurface areas where soil, sand, and rock strata are fully saturated. Groundwater is recharged by surface water to form a contiguous natural water resource. Many groundwater supplies are not treated before consumption.
Natural water is not pure and contains many substances such as calcium, sodium, and organic matter. Although these 'impurities' are naturally occurring, many contamination events are due to human activities and manipulation of the natural environment.
Public and Private Water Supply Systems
People get their tap water from either a public or private water supply system. A public water supply system is defined in the Safe Water Drinking Act of 1974 as '...a system that 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 (3). Urban areas are served by public water supply systems. Public water supplies must meet certain standards as defined in the Safe Drinking Water Act (1974). They are monitored to assure maximum contaminant levels are not exceeded . Private water systems are generally in rural areas and consist of wells which serve one or a few households. Wells are fed by ground water sources which may be replenished by nearby surface water sources. Private well owners are responsible for the quality, testing, and treatment of their water.The quality of drinking water depends upon the water source, the distribution system, the treatment of the water, management, and other environmental factors.
1. Water Resources, Office of Wetlands, Oceans, and Watersheds. Environmental Protection Agency. 6/14/96. URL: http://www.epa.gov/OWOW/indic/II.html
2. A Citizen's Handbook on Groundwater Protection. 1984. Wendy Gordon, Natural Resources Defense Council, Inc. New York, NY. pp.1
3. SDWA, section 1401(4), 42 U.S.C. section 300f(4).
4. EPA. Index of Watershed Indicators. Rev.
September 8, 1997. URL:
This page was prepared by T.L.
Pedersen , June 1997, UCD EXTOXNET FAQ Team.
Revised by B.T. Johnson October 1997.