Municipal Affairs and Environment

Arsenic in Well Water

What is arsenic? 

Arsenic is a semi-metallic element with the symbol "As." This substance is sometimes found to occur naturally in rocks and soils. Arsenic is a well known poisonous substance and is classed as being carcinogenic to humans. It occurs within organic compounds (combined with hydrogen and carbon), and within inorganic compounds (combined within sulphur, chlorine or oxygen). In water, arsenic has no smell or taste and can only be detected through a chemical test. Arsenic concentrations tend to be higher in water from wells than from surface water supplies. The maximum acceptable concentration (MAC) for arsenic in drinking water in Health Canada's Guidelines for Canadian Drinking Water Quality opens new window is 0.010 mg/L. (milligrams per litre)

What are the known sources of arsenic? 

Arsenic is common in the rocks and soils of Newfoundland but does not easily dissolve in water. However arsenic concentrations that exceed the drinking water guideline have been found in public water supplies in several areas of Newfoundland. The arsenic is most likely from natural sources, although arsenic can be produced by human activity such as mine tailings runoff or certain kinds of pressure treated wood. Arsenic is much more likely to be found in water that comes from wells drilled into the bedrock compared to surface water sources or dug wells, especially if the bedrock contains high natural levels of arsenic. The slow movement of groundwater in bedrock allows for long periods of contact between the bedrock and the groundwater. This long contact time allows for the weathering of arsenic bearing minerals and ores dissolving arsenic into the groundwater.

What are the Potential Health Effects?

The primary health concern with exposure to arsenic is cancer. Exposure to arsenic over many years can increase your chances of getting certain types of cancer, or other health effects, such as diarrhea, poor blood production, and abnormal heart beat. The health outcomes depend on the length of time that you are exposed to arsenic from any source, the amount of arsenic in your water, the amount of water that you drink, and your current level of health. The risk of developing health effects are the same for everyone, including children pregnant women and other vulnerable groups.

Where have high arsenic levels been found in Newfoundland & Labrador well waters? 

Research on arsenic in groundwater is being carried out by the Departments of Environment and Mines and Energy under a Memorandum of Agreement between both departments. To date, no arsenic exceedances have been reported for Labrador water supplies. (an exceedance is a test where arsenic values above the MAC guideline value have been found). 

Natural arsenic concentrations in rock vary considerably across the province. Analysis of arsenic values in lake muds allows high natural arsenic areas of the province to be mapped. Research suggests that there is a relationship between high arsenic in lake sediments and elevated arsenic in well water. However elevated arsenic levels in drinking water can be found outside of areas indicated as high in arsenic by lake sediment surveys; and water from most wells in areas known to be drilled into high arsenic bedrock do not contain higher amounts of arsenic.

The following map shows: 

  • areas of the province where elevated arsenic is found in lake sediments. 
  • locations of public and school wells reporting elevated or above the MAC for arsenic.



Areas of Potential Arsenic Concentration in Well Water PDF (265 KB)

The Department of Environment recommends that private well owners in these areas have their well water chemically tested for a standard suite of chemical parameters including arsenic. It is recommended that all well owners have a chemical test done on their well water. Community councils may wish to coordinate water well sampling for their community.

What can well owners do about arsenic contamination of well water? 

If your well water is tested and contains arsenic above the drinking water guideline of 0.010 mg/L, a second test is recommended to verify the original results; in the mean time use bottled water or obtain water from a safe alternate source for drinking and cooking. Arsenic is not removed by pitcher type filtration units or boiling. Water treatment methods that can remove arsenic from well water include reverse osmosis, some filters and distillation units. Homeowners should make sure that any water treatment product used has been certified for the specified purpose by the National Sanitation Foundation (NSF). Monitoring and upkeep of the treatment system is critical and all manufacturer's instructions should be followed carefully. It is recommended that you consult a water treatment specialist before purchasing a treatment device.

Well water testing and source protection 

Private well owners are responsible for the testing of their water well. Government recommends that you test your well water periodically to make sure it is safe to drink. Officials at your local Government Service Centre or the nearest Department of Environment office are available to talk to you about your water supply. Only accredited laboratories are recommended for the chemical testing of drinking water. The following is a partial list of accredited laboratories who can do chemical testing including arsenic. There is a fee for the chemical testing of water.

Accutest Laboratories Ltd.
146 Colonade Rd., Unit 8
Nepean, ON K2E 7Y1
Tel: (613) 727-5692
Fax: (613) 727-5222
Maxxam Analytical Inc.
49-55Elizabeth Ave.
St. John's, NL A1A 1W9
Tel: (709) 754-0203
Fax: (709) 754-8612
Environmental Services Laboratory
Queen Elizabeth II Health Sciences Centre
5788 University Avenue
Halifax, NS B3H 1V81
Tel: (902) 473-8466
Fax: (902) 473-4418


Health Canada, Guidelines for Canadian Drinking Water Quality Supporting Documents."Arsenic." (Aug 2006) opens new window

Health Canada, It's Your Health. "Arsenic in Drinking Water." (May 2006) opens new window

Province of Nova Scotia, Department of Environment and Labour, "Arsenic in Nova Scotia Drinking Water" (Apr 2006) opens new window

Province of Newfoundland and Labrador, Department of Mines and Energy, Geological Survey. Geoscience Atlas of Newfoundland, Open File NFLD/2687. (Sept 1999)

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