Arsenic in Drinking Water: Ontario’s Failure to Endorse Health Canada’s Guideline

Summary: Contaminated drinking water is a threat to public health and quality of life. Despite the fact that most arsenic in drinking water arises from natural sources, it is as important to regulate as industrial sources of any toxic substance. Drinking water contaminated with arsenic has been associated with developmental effects, cancer, cardiovascular disease, neurotoxicity, diabetes and even death. In 2006 Health Canada set a guideline for the Maximum Acceptable Concentration (MAC) of arsenic in drinking water at 0.010 mg/L (or 10 µ/L - micrograms/litre). Ontario’s drinking water standard for arsenic has not been amended to meet this recommendation and remains more than double this level at 0.025 mg/L (25 µ/L). The Canadian Environmental Law Association (CELA) advocates the endorsement of the Health Canada guideline for Ontario’s legally binding standard.

Arsenic – Health Effects: Arsenic is a naturally occurring chemical element widely distributed in the earth’s crust and often found naturally in groundwater thorough erosion of soils, minerals and ores.(1) Most arsenic exposure occurs from naturally contaminated ground water that may be used for drinking water, food preparations, and crop irrigation.(2) Arsenic is highly toxic and a known human carcinogen; exposure to any level of arsenic in drinking water may increase the risk of cancer. Inorganic arsenic has been classified in Group 1 (carcinogenic to humans) by the International Agency for Research on Cancer (IARC).

Acute arsenic poisoning begins with vomiting, abdominal pain, diarrhea, muscular pain and weakness. These symptoms are often followed by numbness and tingling of the extremities, muscle cramping and death, in extreme cases. Long-term and lower level exposure to arsenic from drinking-water and food can cause skin cancer and skin lesions, and may also lead to lung and bladder cancer.(3) Arsenic has also been associated with developmental effects, cardiovascular disease, neurotoxicity and diabetes. While evidence does not indicate greater risk for subpopulations such as children and infants, their smaller body weight can result in proportionally greater exposure often prompting the need for a more precautionary approach to protect them.(4)

Guidelines for Arsenic in Drinking Water: In May 2006 the Federal-Provincial-Territorial Committee (FPT Committee) on Drinking Water, convened by Health Canada, prepared a guideline-technical document(5) to support a guideline level for arsenic in Canadian drinking water. The document reviews the health risks associated with arsenic in drinking water, focusing on inorganic forms of arsenic. They recommended a guideline for the maximum acceptable concentration (MAC) based upon identified health risks, new studies and approaches as well as limitations of available treatment technology. The focus is on exposure through drinking water via ingestion given that exposure through inhalation and skin contact is considered insignificant. The MAC guideline is 0.010 mg/L (10 μg/L) based on municipal- and residential-scale treatment achievability. It has been approved by both the FPT Committee on Drinking Water, another FPT Committee on Health and the Environment, and as of 2006, is the new federal guideline from Health Canada. Due to the limitations of available treatment technology, the MAC is a higher level than would be associated with an “essentially negligible” risk. The FPT Committee on Drinking Water recommends that every effort should be made to maintain arsenic levels in drinking water as low as reasonably achievable (ALARA).

Ontario’s Drinking Water Standard for Arsenic: Ontario’s legally-binding standard for arsenic in drinking water is 0.025 mg/L as set out in schedule 2 of Ontario Drinking Water Quality Standards Regulation (O. Reg. 169/03) enacted under the Safe Drinking Water Act (2002). The Ontario Drinking Water Advisory Council (ODWAC) sent an arsenic advice letter to the Minister of Environment in 2006 recommending the endorsement of the revised federal guideline.(6) The council concluded that the FPT Committee supporting documentation and rationale represented the best information presently available anywhere in the world. In 2007, Ontario noted that it would review its standard in light of the new federal guidance(7) but as of 2014 has failed to amend the provincial standard.

Solutions: Solutions to address arsenic in drinking water are well-established. Water safety frameworks are necessary during planning, installation and management of all new drinking water sources, especially ones based on surface water and very shallow groundwater. The selection of an appropriate treatment will vary case by case depending on specific characteristics of the raw water supply. It is important to determine if any pretreatment is required as it is critical for ensuring arsenic removal efficacy with subsequent treatment technology. Some of the most practical municipal-scale technologies for the removal of arsenic from drinking water include coagulation/filtration, lime softening, ion exchange, reverse osmosis, activated alumina and manganese greensand filtration.(8) Several detailed analyses on the effectiveness and application of various treatment technologies on arsenic removal are available.(9)

According to data reported in the FPT Committee guideline-technical report, levels of arsenic in Ontario drinking, based on data collected from 1997-2002, ranged from 0.1 to 18 µg/L in treated groundwater and surface water in 726 communities with levels in more than 99% of samples at less than 10 µg/L, the annual average being less than or equal to 0.7 µg/L. Ontario monitoring data submitted by private laboratories were slightly higher with arsenic levels in treated and raw drinking water ranging from less than 2.5 to 68 µg/L for the period 1999-2002, the average value being less than 2.5 µg/L. The higher values came predominantly from wells. These data indicate the need for the lower standard in Ontario given that most results would meet the lower standard and higher results would be caught and could be addressed.


(1) Agency for Substances & Disease Registry (ATSDR). Arsenic Fact Sheet. Available at:

(2) World Health Organization (WHO). “Arsenic” Fact sheet N°372. December 2012

(3) For more information on Arsenic health effects. See: Agency for Substances & Disease Registry (ATSDR). Arsenic: Public Health Statement. <>; Murphy MJ, Lyon LW, Taylor JW (1981) Subacute arsenic neuropathy: clinical and electrophysiological observations. Journal of Neurology, Neurosurgery and Psychiatry, 44:896–900.

(4) Health Canada, Chemical contaminants. “Arsenic.”

(5) Guidelines for Canadian Drinking Water Quality: Guideline Technical Document "Arsenic." Prepared by the Federal-Provincial-Territorial Committee on Drinking Water of the Federal-Provincial-Territorial Committee on Health and the Environment. Health Canada Ottawa, Ontario May 2006.

(6) Letter to The Honorable Laurel C. Broten, Minister of Environment. 28th April 2006.

(7) Ontario government. Drinking water information – about arsenic in drinking water. April 2007.

(8) Health Canada. Guidelines for Canadian Drinking Water Quality.

(9) Pokhrel, D., Viraraghavan, T., and Braul, L. (2005). ”Evaluation of Treatment Systems for the Removal of Arsenic from Groundwater.” Pract. Period. Hazard. Toxic Radioact. Waste Manage., 9(3), 152–157; U.S. EPA (2000) Technologies and costs for removal of arsenic from drinking water. EPA-815-R-00-028, Office of Water, U.S. Environmental Protection Agency, Washington, DC.; Thirunavukkarasu, O.S. and Viraraghavan, T. (2003) Arsenic in drinking water: Health effects and removal technologies. In: Aquatic arsenic toxicity and treatment. T. Murphy and J. Guo (eds.). Backhuys Publishers, Leiden, The Netherlands. pp. 129-138