What Is A Public Water System (PWS)?

The term public water system (PWS) refers to any water system that has 15 or more service connections (hook-ups) or serves 25 or more people. Water systems that serve less than 15 service connections or 25 people are considered private water systems and are not regulated by ADEQ. However, there are resources available to owners of private wells and these non-regulated systems.

Public water systems can be run by cities or towns, by federal or state agencies, by other political subdivisions like water districts and co-ops, or by private, for-profit companies. Regardless of the ownership, these systems must comply with all requirements of the Safe Drinking Water Act.

Categories of Public Water Systems

  • A "community water system" is one that serves 15 or more service connections used by year-round residents or that serves 25 or more year-round residents who use water for drinking, cooking, bathing and cleaning. Community water systems may also serve all the businesses and other water users within their boundaries.
  • A "non-transient, non-community water system" is one that serves 15 or more service connections that are used by the same persons for at least six months per year, or serves the same 25 or more persons for at least six months per year. These water systems supply businesses where people may spend a large percentage of time, but these typically aren't a consumer's primary water source. Examples include schools and hospitals.
  • A "transient, non-community water system" is one that serves 15 or more service connections, but does not serve 15 or more service connections that are used by the same persons for more than six months per year; or one that serves an average of at least 25 persons per day for at least 60 days per year, but does not serve the same 25 persons for more than six months per year. Examples include businesses where the average person will not be drinking the water for long periods of time, such as truck stops, restaurants or campgrounds. Because of the short exposure times involved, typically these systems only monitor for acute contaminants such as nitrates or bacteria.
Community and non-transient, non-community water systems make up the majority of the water systems in Arizona.

Although ADEQ does not regulate private wells, the department encourages well owners to educate themselves about water quality and drinking water health issues. Well owners should investigate adjacent land uses and local geology to determine if any contaminants could be affecting their well. Private well owners are strongly encouraged to collect periodic water samples to test for bacteria and other contaminants. The Arizona Department of Health Services Environmental Laboratory Licensure Program  provides information about laboratories certified to perform drinking water analysis and their procedures.