Fluoride is a compound that contains an ionic form of the element fluorine.  Fluoride occurs naturally in many water sources and is added in the treatment process by many public water systems.  Fluoride in amounts between 0.9 and 1.7 milligrams per liter (mg/L) have been beneficial in reducing tooth decay.  Amounts above 4.0 mg/L may cause bone disease.  Amounts greater than 2 mg/L and less than 4 mg/L can cause discoloration of teeth.  The following document contains information about the levels of fluoride in South Dakota public water systems:



Does the fluoride regulation apply to my water system?

Yes, but only community public water systems serving more than 500 people are required by State law to adjust fluoride levels between 0.9 and 1.7 milligrams per liter (mg/L). 


Frequency of Sampling

Sampling must be done yearly if systems use surface water, or every three years if they use ground water.  If your system is a community public water system over 500 than monthly samples are required. 


Maximum Contaminant Level

Maximum Contaminant Level = 4.0 mg/L (secondary standard suggested level = 2.0 mg/L).If your water system serves less than 500 people and tests show levels less than the 2.0 mg/L, your water system needs to do nothing about fluoride. 


Actions your water system should be taking

If tests indicate fluoride levels between 2.0 and 4.0 mg/L, your water system should check with the Drinking Water Program to see if any changes in operations can be made to lower the fluoride level.  Since this is not an Maximum Contaminant Level violation, immediate action is not required, but planning should be undertaken to reduce levels below 2.0 mg/L.    The Drinking Water Program may require more frequent sampling to monitor the fluoride level.  A quarterly public notice, with mandatory health effects language is required for levels above 4.0 mg/L.  An annual public notice must be issued if the level is between 2.0 and 4.0 mg/L. 


If tests indicate fluoride levels above 4.0 mg/L, your water system is in violation of the Maximum Contaminant Level and they must:

  • Contact the Drinking Water Program.  They will assist with forming the contents of a public notice that is required for their customers (see Public Notification section).Work with the Drinking Water Program and their water manager to plan for a change in your water supply or treatment system to lower the fluoride levels.Seek help through other resources agencies (listed in the Resource Agencies Section of this pamphlet) for help in finding financial resources if need to make water system changes.
  • Continue quarterly testing, as suggested or required by the state agency to monitor fluoride levels while they are working on solutions.  Notify the public quarterly, as required.


Solutions to fluoride Maximum Contaminant Level violations for very small water systems usually involve finding and using a new water source or mixing existing sources to reduce the fluoride level.  Removing fluoride through treatment is usually cost prohibitive for a very small system.Your local dentist or state dental association will have information available on the beneficial effects of correct amounts of fluoride in your drinking water. 


Additional Information