The national legislation first passed by the U.S. Congress and signed into law by the President in 1974 and amended in 1986. The SDWA directs the U.S. Environmental Protection Agency to promulgate and enforce standards for safe drinking water necessary to protect public health at public water systems serving 25 or more people for an average of 60 days per year. The law also contains provision for delegating primary enforcement responsibility to states and for protecting underground sources of drinking water.