Nitrate in Drinking Water
Nitrate is a chemical compound that occurs naturally throughout the environment in groundwater, plants including fruits and vegetables or may be present due to human activities. Nitrate is formed when nitrogen combines with oxygen or ozone. Nitrogen is essential for all living things, but high levels in drinking water can be harmful to health, especially for infants.
Nitrate can occur naturally in surface and groundwater at low levels that do not cause health problems. However, high levels of nitrate in surface and groundwater can result from agricultural runoff, improper well construction, natural decay of organic matter in groundwater and leaking septic systems.
Water wells that are shallow, dug, bored or prone to flooding may be more vulnerable to such contamination.
The Ontario Drinking Water Quality Standard for nitrate is 10 milligrams per litre (mg/L) measured as nitrogen. This is the maximum acceptable concentration (MAC) for nitrate drinking water.
Potential health effects of nitrates in drinking water depend on how much nitrate a person is exposed to, how long they were exposed, their age, and pre-existing health conditions. The level of nitrates most people are exposed to would not cause adverse health effects.
Exposure to an elevated level of nitrate in drinking water is primarily a health concern for bottle-fed infants less than six months of age who have not yet developed the ability to properly digest nitrate. This can lead to a rare but very serious condition called methemoglobinemia or blue-baby syndrome. Methemoglobinemia impacts the delivery of oxygen to tissues in the body, resulting in a bluish skin colour, particularly around the mouth and eyes due to a lack of oxygen.
Other susceptible individuals include pregnant women and people with certain blood disorders.
If the level of nitrate in your water is above 10mg/L, you should use a different water supply to prepare baby formula and food or use ready-to-use formula. Breastmilk is not affected by nitrates and is considered safe.
Nitrates have also been classified as a possible carcinogen by the International Agency for Research on Cancer (IARC) if they undergo changes in the body that result in the formation of N-nitroso compounds. The extent to which this reaction occurs in the body is influenced by long-term consumption of high levels of nitrates that exceed drinking water guidelines and diet. Research continues to explore the effects associated with long-term consumption of nitrates and some cancers.
Nitrate is a colourless, tasteless, and odourless compound. The only way to know whether there is nitrate in your drinking water is to have it tested by a licensed laboratory. Municipal drinking water systems are required to be tested regularly. If you draw your drinking water from a well, the health unit recommends testing your well water for nitrate at least once a year, especially if anyone consuming the water is pregnant or under the age of one. Visit the Ministry of the Environment, Conservation and Parks website for a complete list of accredited laboratories.
It is also recommended that you test your well water for bacteria at least three times a year. Bacterial contamination can be an indicator that surface water is entering your well which may also contain nitrate.
Sodium in Drinking Water
Sodium is a nutrient found in table salt and many other foods. Your body needs some sodium to function, but too much may lead to high blood pressure (a major risk factor for stroke, heart disease and kidney disease). Most Canadians take in more than twice the amount of sodium they need in a day.
For a healthy adult, the level of sodium in the water supply does not pose a risk to health. However, if you or members of your family have kidney disease, heart disease, high blood pressure or liver disease, and need to restrict your salt intake because of these illnesses, please ask your physician or health care professional how sodium in the water may affect your health.
The Guidelines for Canadian Drinking Water Quality and Ontario Drinking Water Quality Standards set an aesthetic objective for sodium in drinking water at 200 mg/L, at which point it can be detected by a salty taste by the average person. A maximum acceptable concentration for sodium in drinking water has not been specified.
The Safe Drinking Water Act, the Ontario Drinking Water Systems Regulation (Ontario Regulation 170/03), requires that a report be made to the local Medical Officer of Health if a sodium result is higher than 20 mg/L in a sample of drinking water so that local physicians and other health professionals can be advised of this to help those on sodium restricted diets control their sodium intake.
Healthy adults (14-50 years old) should consume between 1500 and 2300 mg of sodium each day; however, for individuals on sodium restricted diets, the amount of sodium in the water may be significant. When sodium levels in drinking water are at 20 mg/L, drinking 2 litres per day would contribute 40 mg of sodium to a person’s diet.
For healthy adults, this level of sodium in drinking water does not pose a health risk; however, for people on a very strict sodium restricted diet of 500 mg per day, this would contribute about 8% of their daily sodium allowance.
When sodium levels are higher than 20 mg/L, the Medical Officer of Health is required to inform the public, through health professionals, in order to help people on sodium-restricted diets control their sodium intake.
The bacteriological safety of municipal drinking water is not affected by sodium levels, meaning that the water is safe to drink.
In Ontario, sodium is required to be sampled in municipally treated drinking water every five years. In addition, all sodium levels in excess of 20 mg/L must be reported to the Medical Officer of Health.
The Haldimand-Norfolk Health Unit periodically notifies local physicians of elevated sodium levels in our municipal drinking water in order for them to advise their patients with sodium-restricted diets accordingly. For the latest reports of sodium levels in your municipal drinking water, visit the links below:
For Haldimand County
For Norfolk County
For more information about water testing for wells, cisterns, and other private water systems, visit