Final answer:
The Environmental Protection Agency (EPA) is the U.S. government agency responsible for setting water quality standards through legislation such as the Safe Drinking Water Act and subsequent amendments, enforcing standards, monitoring public water systems, and regulating contaminant levels.
Step-by-step explanation:
The United States government agency that is responsible for water quality standards is the Environmental Protection Agency (EPA). The EPA gained significant authority in regards to water quality through the Safe Drinking Water Act of 1974, which enabled it to set standards for public water systems servicing over 25 people. States were still tasked with the implementation and enforcement of these drinking water standards. With the creation of Maximum Contaminant Level (MCL) and Treatment Technique (TT) guidelines, the EPA defined the acceptable levels of contaminants within water sources.
Subsequent amendments, like those in 1986 and 1996, further strengthened the SDWA, by regulating more contaminants, installing additional monitoring devices, enhancing pathogen detection, and ensuring public notifications during severe water quality issues. Additionally, more protections and assessments were introduced for water sources such as lakes, rivers, and streams, and water companies were mandated to supply consumers with a water quality report.