Inorganic Contanimants

Inorganic Contaminants (IOCs) are elements or compounds found in water supplies and may be natural in the geology or caused by activities of man through mining, industry or agriculture. It is common to have trace amounts of many Inorganic Contaminants in water supplies. Amounts above the Maximum Contaminant Levels may cause a variety of damaging effects to the liver, kidney, nervous system circulatory system, blood, gastrointestinal system, bones, or skin depending upon the inorganic contaminant and level of exposure. Some Inorganic Contaminants are more damaging to infants and pregnant women. Because of some special aspects of the rules for asbestos, fluoride, and nitrates, separate pages can be found for them on this web site.

This rule includes community and non-community systems that use groundwater sources. Groundwater sources include wells, springs, galleries, and any other water sources that are not regulated under the Surface Water Treatment Rule. Systems must comply with the requirements of the GWR beginning December 1, 2009.

There are three major areas of concern for your system-

Do the inorganic contaminant regulations apply to my water system?

Yes, all community and non-transient non-community public water supply systems must monitor for regulated Inorganic Contaminants in their water supply. At the present there are 15 regulated Inorganic Contaminants (including fluoride, arsenic, and nitrates).

  • Samples are to be taken at the entry point where the source enters the distribution system after treatment.
  • Samples must be taken to an EPA approved laboratory for analysis.
  • Sampling continues yearly or every three years for currently regulated Inorganic Contaminants.
  • Ground water systems - sample every 3 years
  • Surface water supplies - sample annually
  • Waivers are available to reduce inorganic contaminant sampling to once every nine years.

Frequency of sampling

  • Notify the Drinking Water Program and complete Public Notices as required
  • Work with the Drinking Water Program to determine the best way to reduce the level of contaminant in your water supply. A variety of options can be considered including a new treatment process, mixing your contaminated supply with another supply that does not exceed the Maximum Contaminant Level, or using a new source of water.
  • Contact resource agencies listed on the Resource Agencies page of this web site for help in planning and finding financing for your system improvements.
  • Monitor quarterly.

Inorganic Contaminants With Maximum Contaminant Levels

Antimony 0.006 mg/L
Arsenic 0.01 mg/L
Asbestos 7 million fibers/L
Barium 2 mg/L
Beryllium 0.004 mg/L
Cadmium 0.005 mg/L
Chromium 0.1 mg/L
Cyanide 0.2 mg/L
Fluoride 4 mg/L
Mercury 0.002 mg/L
Nickel 0.1 mg/L
Nitrate 10 mg/L
Nitrite (as N) 1 mg/L
Nitrate & Nitrite (combined) 10 mg/L
Selenium 0.05 mg/L
Thallium 0.002 mg/L

Additional Information

The rules for Inorganic Contaminants are contained in 40 CFR 141.11, 141.23, 141.62.