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The purpose of the law is to assure that the nation 's water supply systems serving the public meet minimum national standards for the protection of public health . By some estimates it contributes 80 % of the contamination that is found in this nation 's water resources . The investment cost to shore up the nations ' water treatment facilities are high , but the potential costs of not doing so are even greater . The concealment or playing down of these facts ( quite probably for Political reasons ) constitutes a grave dereliction of duty by those formerly charged with the fate of nation 's water system . The public strongly supports federal funding to invest in the maintenance and improvement of the nation 's water treatment infrastructure . The National Water-Quality Assessment ( NAWQA ) program of the U.S. Geological Survey aims to provide a nationally consistent description of current water quality conditions for a large part of the Nation 's water resources ; to define long-term water quality trends where possible ; and to identify , describe , and explain these conditions and trends . These declines are a good indication that the switch to unleaded gasoline in the late 1970s , coupled with enactment of the Clean Air Act , have produced a positive effect on the nation 's water resources . Statistical analyses of streamflow have extensive applications to the design of the State 's and Nation 's water resources and transportation infrastructures , including water-supply systems , flood-hazard mitigation measures , highway bridges , culverts , navigation systems , and many others .