Why only in theory? The truth is that some of Earth's liquid fresh water can no longer support life because it is contaminated with harmful elements that cause illness or death if ingested. So, while one percent of Earth's total water might have been available for living organisms at one time, recent human activity has rendered a portion of that one percent undrinkable. How did this happen?

The portion of Earth's freshwater supply that is found in streams, rivers, and lakes is called surface water. (Ground water, and the water in the polar caps, glaciers, soil, and atmosphere, though also fresh, is not considered surface water.) It is from surface-water sources that most U.S. communities draw water for everyday use.

Clean surface water has been a concern of U. S. legislators since the 1950s and1960s, when it was observed that fish were dying in the nation's lakes. The Clean Water Act of 1972 requires that each state conduct water quality surveys to determine the overall health of its surface water supplies. Every two years the states must report their findings to the Environmental Protection Agency (EPA), which in turn prepares a biennial report to Congress. The report is a complete and up-to-date snapshot of water quality conditions throughout the country.

The states, Native American Tribes, and other jurisdictions also define appropriate uses for surface water and consider these uses when outlining water quality standards, which are then presented to the EPA for approval. One reason for these standards is to promote safe living conditions for aquatic life. These conditions, in turn, lead to fish and shellfish that are fit for human consumption and to clean water for drinking, swimming, boating, fishing, and agricultural irrigation.

Once a concern mainly of the states and federal agencies, the scarcity of clean surface water has recently attracted the attention of local communities, and more local agencies have been taking an active part in monitoring this vital commodity. In fact, your own local agency has asked your company to develop a program for monitoring the quality of the surface waters within your community's watersheds. By examining the various methods of monitoring water quality provided by the following case studies, you and your colleagues will prepare a report, with supporting rationales, containing recommendations on where, when, and how to best monitor the surface water quality in your community's watersheds.

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