Which standard is used in the United States to define safe drinking water?

The correct answer is the National Primary Drinking Water Regulations. These regulations set the enforceable standards for drinking water quality in the United States. They specify the maximum contaminant levels for various substances that could pose a risk to public health, ensuring that the water is safe for consumption. The regulations are developed under the authority of the Safe Drinking Water Act, which serves as the main framework for overseeing public drinking water systems.

The National Clean Water Act primarily focuses on regulating discharges into bodies of water to maintain and improve the quality of surface waters, rather than drinking water specifically. Environmental Protection Agency (EPA) guidelines may provide additional recommendations and best practices but are not enforceable standards like the National Primary Drinking Water Regulations. The Safe Drinking Water Act is crucial as it provides the legal basis for establishing these primary regulations, but it is the regulations themselves that define safe drinking water standards applicable to public water systems.