Primary Inorganic Chemicals

Primary inorganic chemicals (PIOC) refers to all inorganic contaminants regulated under the National Primary Drinking Water Regulations Chemical Contaminant Rules (also known as the Phase II/IV Rules). All community water systems and non-transient non-community water systems, which have their own source, must comply with the PIOC standards.

Olivia Griffith

Rule Manager

P: 701-328-6624

Fact Sheet


  • What are inorganic chemicals?
    • Inorganic chemicals are metals, salts, and other compounds that do not contain carbon. These chemicals sometimes contaminate water supplies because of human activity; however, many are naturally occurring in certain geographic areas.
  • What are the maximum contaminant levels (MCL), maximum contaminant level goals (MCLG), possible health effects and sources for the PIOCs?
  • Where and how often do samples for PIOCs need to be collected?
    • Sampling for PIOCs must be taken at the entry point to the distribution system after all treatment. The Standardized Monitoring Framework established by the U.S. EPA is followed for compliance cycles. Sampling for ground water systems is required once every three years and for surface water systems once every year. Sampling requirements will increase for any water system with a result at or above the MCL. Waivers may be issued to reduce the frequency of sampling to once every nine years.