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Drinking Water

Ontario Drinking Water Standards Regulation 170/03 under the Safe Drinking Water Act, 2002, requires routine monitoring of sodium in drinking water systems.  Many drinking water systems in Simcoe County and the District of Muskoka have elevated levels of naturally occurring sodium. Adverse reports of sodium in drinking water are reportable to the Medical Officer of Health, who in turn must share this information with physicians, who may need to consider the potential impact on their patients. 


  • Concentrations in exceedance of 20 milligram per litre (mg/L) are reportable to the Medical Officer of Health
  • There is no Maximum Acceptable Concentration (because sodium is not a toxic element)
  • Frequency of testing required every 5 years under Regulation 170/03
  • The aesthetic objective is 200 mg/L or less (detectable by taste beyond that level)

Clinical Implications

  • Sodium concentrations in drinking water are not a concern for most people
  • Elevated sodium concentrations in drinking water may have implications for individuals with the following medical conditions:
    • Poorly controlled or severe hypertension
    • Congestive heart failure
    • Other medical condition requiring a sodium restricted diet
    • Infants
  • For example, drinking 2 liters of water at a sodium concentration of 20 mg/L in a day would contribute 40 mg of sodium to daily sodium intake. This represents 8% of sodium intake for patient on a sodium restricted diet of 500 mg/day. While small relative to other sources of sodium, drinking water sodium concentration should still be considered in those with severe salt restrictions, particularly if levels are in exceedance of 20 mg/L.
  • Water softeners can increase sodium levels in drinking water. They should be avoided by individuals on a salt restricted diet and in infants (including for the preparation of infant formula).

Sampling Results

  • To advise patients about sodium levels in drinking water, please see the table below, which lists drinking water systems in Simcoe County and the District of Muskoka reporting with sodium levels that exceed 20 milligrams per litre in the past five years.
  • If results from a specific drinking water system (non-private) are needed, please contact the Simcoe Muskoka District Health Unit Health Connection at 705-721-7520 or toll-free at 1-877-721-7520 to speak with a public health inspector or contact your local municipality.
  • Private well owners can test their drinking water for bacteria free of charge by retrieving a water sample bottle for testing from a local health unit office. If they wish to sample for any other parameters such as sodium they will have to contact a private licensed laboratory. A list of private licensed laboratories is available at:

Listing of Sodium Exceedances

Additional Resources

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