Which of the following is a requirement for all public water systems under the Safe Water Drinking Act?

Maintaining a comprehensive monitoring plan is a fundamental requirement for all public water systems under the Safe Drinking Water Act (SDWA). The SDWA aims to protect public health by regulating the Nation's public drinking water supply. This includes the necessity for water systems to regularly monitor water quality, ensuring that it meets safety standards established by the Environmental Protection Agency (EPA).

A comprehensive monitoring plan typically encompasses various aspects, such as routine testing for microbial contaminants, chemical pollutants, and overall water quality parameters. This ensures that any potential health risks are identified and addressed promptly, thereby safeguarding the health of the consumers relying on that water supply.

Other options, such as installing a water softener or conducting monthly testing for every chemical, do not represent universal requirements applicable to all public water systems. Similarly, offering public tours of water facilities, while it may be a best practice for transparency and public engagement, is not mandated by the SDWA.