P.L. 93-523 (December 16, 1974) as amended, is the key federal law for protecting public water systems from harmful contaminants. First enacted in 1974, the Act, as amended, is administered by the Environmental Protection Agency through regulatory programmes that establish standards and treatment requirements for drinking water contaminants, control underground injection of wastes that might contaminate water supplies, and protect ground and surface water sources. Regulated public water systems under the Act are those that have at least 15 service connexions or regularly serve 25 or more individuals. The 1996 amendments (P.L. 104-182) broadened the definition of "public water system" to include systems that deliver water through pipes or "other constructed conveyances," which includes agricultural irrigation systems that convey water that is used for residential purposes (unless alternative water is provided for drinking and cooking; or unless water for drinking, cooking, and bathing is treated). The 1996 amendments also require states to identify, to the extent practicable, origins of contaminants in areas providing source waters for public water systems to determine the susceptibility of systems to contamination; such areas could include farmland.