Sodium in London Drinking Water
Consumers of food and water have become more conscious of the amount of sodium that they ingest, especially for those individuals on sodium restricted diets. The information below is intended to assist London customers determine the contribution from drinking water to their total sodium dietary intake. Recently the water supplied to London from the Elgin Area Primary Water Supply System exceeded the mandatory reporting limit of 20 mg/L for sodium. Drinking water with sodium concentration greater than 20 mg/L is common in many other municipalities in Ontario. The amount of sodium in London’s drinking water does not pose a health risk to our customers and in fact the province has not established a health related standard for sodium in drinking water.
What is sodium?
Sodium is a naturally occurring mineral in food and water, and is a necessary element of human nutrition. Typically the consumption of sodium from food is much higher than from drinking water.
How does sodium get into the drinking water?
Sodium in raw water sources can vary dramatically depending on the source – lakes, rivers or wells. The naturally occurring sodium levels in lakes Huron and Erie range between 4 mg/L and 14 mg/L. The total amount of sodium in drinking water results from the amount in the source water and the sodium added from the water treatment process.
How much sodium is acceptable in drinking water?
The Guidelines for Canadian Drinking Water Quality and Ontario Drinking Water Quality Standards (ODWS) set an aesthetic objective (non-health related) for sodium in drinking water at 200 mg/L, at which point it can be detected by a salty taste by the average person. The province has not specified a health related maximum acceptable concentration in drinking water in the ODWS.
Under the Safe Drinking Water Act, the Ontario Drinking Water Systems Regulation (170/03) requires that a report be made to the local Medical Officer(s) of Health if a sodium result exceeds 20 mg/L in a sample of drinking water. When a sodium sample result in drinking water exceeds 20 mg/L, the Medical Officer of Health informs physicians and other health professionals to help people following sodium restricted diets determine their sodium intake.
How much sodium is in drinking water supplied to London?
The City of London receives water from both the Lake Huron Primary Water Supply System, and the Elgin Area Primary Water Supply System. More detailed information on these systems can be found on the Regional Water website.
The natural sodium concentration in Lake Erie water can range from 8 to 14 mg/L, and the water treatment processes add more sodium to the natural lake amounts. In 2013, the sodium level in the treated Elgin water has ranged from 19 mg/L to 21 mg/L. By comparison, the sodium level in the treated water received from Lake Huron is typically between 10 and 11 mg/L, below the notification limit of 20 mg/L. Sodium levels above 20 mg/L are not uncommon in drinking-water; in fact, several nearby municipalities in Southwestern Ontario have sodium levels that regularly exceed 50 mg/L.
London receives approximately 15% of its water from the Elgin System, and this water feeds into southeast London. The water from the Elgin System is pumped into the same network of water mains as the water from the Huron System, and there are no fixed boundaries between the Huron water and the Elgin water. In fact, the zone where the two water sources meet and mix is constantly in a state of transition, depending upon how much water customers are using and pumping rates from the two systems. People in north London receive primarily Lake Huron water, and people in the very southern limits of London receive Elgin water; in between, there is a mix of water from both supply systems. The Elgin water can extend as far north as Byron Baseline Rd. and Springbank Dr. in the west end of London, and Oxford St. E. in the east end of London. As one travels south from these general boundaries, the proportion of Huron water decreases as the proportion of Elgin water increases, resulting in sodium increasing slightly from 11 mg/L to 21 mg/L from north to south.
How will sodium levels greater than 20 mg/L affect my health?
The human body requires sodium to maintain blood pressure, control fluid levels and for normal nerve and muscle function. Health Canada advises that healthy adults (14-50 years old) should consume between 1,500 and 2,300 mg of sodium each day; however, individuals on sodium restricted diets should consider the amount of sodium in the water when calculating their sodium intake. 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; for people on a very strict sodium restricted diet of 500 mg per day, this would contribute about 8% of their daily sodium allowance.
Other sources of sodium
Food products, not water, are the major dietary sources of sodium. Sodium is also found in drugs such as antacids, laxatives, aspirin and cough medicines, as well as table salt. One teaspoon of table salt contains 2300 mg of sodium. Municipal tap water at 20 mg/L has a relatively low sodium content when compared with other beverages. For example, Health Canada reports the following sodium concentrations for some common beverages:
Cola – 40 mg/L
Ginger-ale – 72 mg/L
Sports Drinks – 404 mg/L
Skim Milk – 436 mg/L
Chocolate Milk (1%) – 644 mg/L
Tomato Juice – 2,760 mg/L
Carrot Juice – 2,912 mg/L
Chicken Broth – 3,224 mg/L
Guidance on calculating sodium intake from London Water
People on sodium restricted diets should estimate the amount of water they consume daily including coffee, tea and other tap water sources in litres of water. Multiply the litres of water by either 11 mg per litre in north London, north of the boundary noted above or 21 mg/L in south London to be safe in your calculation. Subtract this amount from your daily allowable sodium intake; the difference is the amount of sodium that may be consumed from food and other beverages. We recommend that you confirm this approach with your health care professional.
References and Additional Information
Health Canada - Canadian Nutrient File
Dietitians of Canada
Ontario Ministry of Health and Long Term Care
Health Canada – Nutrient Value of Some Common Foods
For further information on the health effects of sodium, please contact your health care professional or:
Middlesex-London Health Unit
Environmental Health Team, Ext. 2300
Public Health Dietitian, Ext. 2222