Community groups and public water systems are often especially involved in the second step of an assessment -- identifying potential sources of pollutants that could contaminate the water supply. This inventory usually results in a list and a map of facilities and activities within the delineated area that might release contaminants into the ground water supply (for wells) or into the watershed of the river or lake (for surface water sources).
Some examples of potential pollutant sources are landfills, underground or aboveground fuel storage tanks, residential or commercial septic systems, stormwater runoff from streets and lawns, farms that apply pesticides and fertilizers, and sludge disposal sites.