a healthy ocean environment. The Point Loma plant uses an advanced primary process. The requirement to perform secondary treatment on wastewater before ocean discharge was waived by the EPA in 1995, "taking into account the city's unique circumstances". In 1987 Congress passed the Water Quality Act, which replaced the construction grant program with a system of subsidized loans using the Clean Water State Revolving Fund (CWSRF). The intention at the time was to completely phase out federal funding after a few years. Funding peaked in 1991 and continued at high levels thereafter, despite the original intentions. New challenges arose, such as the need to address combined sewer overflows for which EPA issued a policy in 1994. In 1996 Congress established the Drinking Water State Revolving Fund, building on the success of the CWSRF, in order to finance investments to improve compliance with more stringent drinking water quality standards. Technical and environmental overview This section provides a brief overview of the water supply and sanitation infrastructure in the U.S., water sources of some of the main cities, and the main types of residential water use. Infrastructure The centralized drinking water supply infrastructure in the United States consists of dams and reservoirs, well fields, pumping stations, aqueducts for the transport of large quantities of water over long distances, water treatment plants, reservoirs in the water distribution system (including water towers), and 1.8 million miles of distribution lines. Depending on the location and quality of the water source, all or some of these elements may be present in a particular water supply system. In addition to this infrastructure for centralized network distribution, over 13 million households rely on their own water sources, usually wells. The centralized sanitation infrastructure in the U.S. consists of 1.2 million miles of sewers—including both sanitary sewers and combined sewers, sewage pumping stations and publicly owned treatment works (POTW). EPA estimated that there were at least 16,583 POTWs operating in 2004, serving a population of 222.8 million. About 860 communities in the U.S. have combined sewer systems, serving about 40 million people. In addition, at least 17% of Americans are served by on-site sanitation systems such as septic tanks. In the United States over 75 percent of the population is served by over 16,000 municipal sewage treatment plants. Most plants are required to meet national secondary treatment standards. Water sources About 66% of the U.S. population (195 million people)