Final answer:
The Environmental Protection Agency (EPA) determines the definition of potable water in the United States, guided by the Safe Drinking Water Act (SDWA) and subsequent amendments, setting criteria such as Maximum Contaminant Levels.
Step-by-step explanation:
The organization that determines the definition of potable water in the United States is the Environmental Protection Agency (EPA). The EPA was given this authority with the enactment of the Safe Drinking Water Act (SDWA) in 1974. Under this act, the EPA has set forth water quality standards that include criteria to protect drinking water sources and establish Maximum Contaminant Levels (MCLs) and Treatment Techniques (TTs) to ensure water safety for public consumption. The regulations have evolved, making water quality standards more rigorous, as noted by laws such as the Clean Water Act and later amendments to the SDWA. These efforts are part of a broader mission to protect human health and the environment, ensuring that citizens have access to safe, clean, and potable water.