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Arsenic in drinking water

Arsenic is a substance found in rocks and soil that occurs naturally. People can be exposed to many forms of arsenic, and arsenic is broadly grouped into 2 categories:

  • organic (meaning that it is combined with carbon) 
  • inorganic (meaning it is not combined with carbon)

Organic arsenic, such as that found in fish, is considered safe. Inorganic arsenic is not.

  • How you’re exposed to arsenic

    Canadians may consume arsenic from their municipal drinking water or private well water, but usually these levels are very low. But some areas of Canada have higher levels of arsenic in drinking water. Arsenic gets into drinking water either from natural sources, such as rocks and soil, or by contamination from certain types of mining, smelting or manufacturing plants. Canadians could be exposed to unsafe amounts of arsenic if they drink water that has a high level of arsenic.

    Showering, bathing, swimming and other activities involving water are not believed to be harmful because arsenic is not absorbed through the skin.

    Other sources of exposure
    You may also be exposed to arsenic from CCA-treated wood or by inhaling pollution from certain types of mining, smelting or manufacturing plants that release arsenic into the air. But this exposure is much less than through drinking water that contains arsenic.

  • Arsenic and cancer

    The International Agency for Research on Cancer (IARC) classifies arsenic in drinking water as a known cause of cancer. Find out more about how cancer-causing substances are classified.

    Drinking water that is contaminated with a high level of arsenic over a long period of time is known to increase the risk of several types of cancer, including lung, bladder and certain types of skin cancers.

  • Tips to reduce your exposure

    If you have a private well, test it for arsenic. Your provincial or territorial health and environment ministries can tell you how to do this. If your arsenic level is above 0.01 milligrams per litre (0.01 mg/L) or 10 micrograms per litre (10 µg/L), stop drinking from the well and take steps to reduce the level of arsenic.

    You can get information about reducing the arsenic levels in residential water treatment systems from Health Canada or the National Sanitation Foundation (US).

    The Canadian Cancer Society does not recommend using bottled water over tap water unless your tap water contains high levels of arsenic. There is no evidence that bottled water is safer than tap water. In fact, there is a proposal to update the current regulations for bottled water so that they are similar to the guidelines for tap water, which are based on more current scientific information. Other bottled drinks are regulated in a similar way.

    If your water is contaminated with arsenic, bottled water can be a substitute source for water until the arsenic problem is resolved. To find out more on bottled water safety, see Health Canada’s website.

  • Suggested links for more information

    General information about arsenic in drinking water
    Learn more about sources of arsenic exposure, potential health risks associated with arsenic exposure, and the role of government in regulating drinking water standards in Canada and the US.

    Health Canada – Arsenic in drinking water
    CAREX Canada – Carcinogen profile: arsenic
    US Environmental Protection Agency – Arsenic in drinking water
    US Environmental Protection Agency – Just the facts for consumers: arsenic in your drinking water (PDF)
    World Health Organization – Arsenic in drinking water

    Drinking water protection
    These materials prepared by Canadian governmental agencies provide information and guidance on keeping our drinking supplies safe.

    Health Canada – Canadian drinking water guidelines
    Health Canada – From source to tap: guidance on the multi-barrier approach to safe drinking water
    Health Canada – Frequently asked questions about bottled water

    Science-based evaluations of arsenic
    These websites discuss the scientific evidence on arsenic and cancer.

    International Agency for Research on Cancer – Evaluation of drinking water and contaminants, including arsenic
    World Health Organization – United Nations synthesis report on arsenic in drinking water

    Occupational exposure to arsenic
    Detailed information about health and safety issues associated with exposure to arsenic in the workplace.

    US Department of Labor, Occupational Safety and Health Administration – Arsenic



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