Selenium in Drinking Water

Selenium is a naturally occurring element that is widely distributed throughout the Earth’s rocks and soils and is found in trace quantities in most plant and animal tissues. Selenium can be dissolved by weathering of minerals in the soil or rock or deposited from atmospheric sources and be present in groundwater. The concentration of selenium in natural waters is typically very low but can vary depending on the nature of local rocks and soils, and food is the main source of intake for most individuals.

What are the health concerns?

Selenium is considered to be an essential nutrient for human health at low levels, but consumption at very high concentrations (above 9 mg/L) over a period of days or weeks can cause nausea, diarrheal, vomiting, fatigue and irritability. Long term exposure at lower concentrations can cause hair and fingernail damage or damage to liver tissue. To minimize the risks associated with long term exposure to selenium, the Guidelines for Canadian Drinking Water Quality, published by Health Canada, recommend that selenium concentrations in drinking water should not exceed 0.05 mg/L. This means that no adverse health effects would be expected from the ingestion of drinking water containing selenium at this level over a lifetime (70 years). 

The drinking water guideline for selenium is based on life time exposure, and for short term exposure to drinking water moderately above the drinking water guideline of 0.05 mg/L the first step should be to follow-up by re-sampling the water supply to confirm the initial results. However, in the event that testing shows ongoing elevated levels of selenium, there are several options available including switching to an alternate source of water, treating the water in your well to reduce selenium levels, or if no other options are available, use bottled water for drinking and food preparation. Bathing or showering with water that contains selenium is not a health concern.

What are the treatment options?

There are drinking water treatment devices available to reduce the levels of selenium in drinking water to levels below the guideline level of 0.05 mg/L. A water treatment professional should be consulted for advice on your particular situation. The most common and effective methods include reverse osmosis or distillation. 

The Department does not recommend specific brands of treatment devices; however, it is recommended that consumers purchase devises bearing a label that indicates it has been certified to NSF/ANSI Standard 58 for Reverse Osmosis Drinking Water Treatment Systems or NSF/ANSI Standard 62 for Drinking Water Distillation Systems. 

As with the use of any drinking water treatment device, the effectiveness of treatment should be verified by sampling after installation. In addition, it is important to ensure the device is used and maintained according the manufacturer’s directions and its performance periodically confirmed by sampling. 


Published date: 
February 5, 2024
Environment, Energy and Climate Action

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