The Status of Drinking Water in Ontario, Canada (1992-1999)

Article excerpt


Objective: This study was conducted to investigate the characteristics of public water works (PWW) in southern Ontario with respect to their water sources and treatment regimes.

Methods: Data from 481 PWW covering the period 1992-1999 were collected and cartographic manipulations as well as descriptive analyses of the PWW attributes were performed. Tests of associations between different PWW attributes were done using Fisher's Exact test and Cochran-Mantel-Haenszel statistics.

Results: Water sources for the PWW included surface water (SW) (21% lakes; 13% rivers), ground water (GW) (64%) and mixed sources (2%). Most (81%) of the population was supplied with SW. Filtration was performed by 84% and 8% of the PWW using SW and GW, respectively. Similarly, disinfection was performed by 99% and 91% of the PWW using SW and GW respectively. There was no significant difference in treatment regimes between PWW in urban and those in rural areas but treatment regime was a function of water source. Overall, most PWW (87.8%) met the minimum treatment requirements of the then Ontario Drinking Water Objectives (ODWO).

Discussion: The study shows that most PWW complied with the minimum treatment requirements of the then ODWO.1 The minimum treatment required by the ODWO was disinfection for GW and both disinfection and filtration for SW. The non-compliant PWW will need to comply for continued provision of safe drinking water. Suffice it to say that both watershed protection and improved water treatment will be imperative for the continued provision of safe drinking water and control of waterborne diseases.

Safe drinking water continues to be a subject of concern for many Canadians.2-6 The quality of drinking water depends on the source and treatment process. If the sources are not adequately protected, contamination by pathogenic organisms may result.7,8 Improper treatment may lead to adverse exposure of the population to pathogenic organisms, and accompanying health risks. Moreover, chlorination alone does not provide adequate protection against all waterborne diseases since a significant proportion of cases may be due to protozoa (e.g., Cryptosporidium) that are resistant to normally acceptable levels of chlorine.9

In Ontario until recently, there have been no laws governing treatment of drinking water by public water works (PWW).10,11 Drinking water quality standards were based only on guidelines, which were not legally binding and yet drinking water has been a source of major outbreaks of gastrointestinal infections in Canada.1 Examples include outbreaks of E.coli O157:H7 in Walkerton, Ontario3 as well as the cryptosporidiosis outbreaks in Cranbrook and Kelowna, British Columbia8 and North Battleford, Saskachewan.12 These incidences have aroused much interest in the quality of drinking water. This study was conducted to investigate the characteristics of PWW in southern Ontario with respect to their water sources and treatment regimes in order to assess the proportion of PWW not meeting the minimum water treatment requirements of the Ontario Drinking Water Objectives (ODWO).1 In Ontario, a PWW is any water works capable of supplying water at a rate greater than 50,000 litres per day and serves more than five private residences.1


Data collection

A database containing water attribute and distribution information from 481 PWW in Ontario was compiled for the years 1992-1999. Attribute data, including water sources, treatment regimes and population served by each PWW during 1999, were obtained from the Ontario Ministry of the Environment and Energy. Attribute data for the years 1992-1998 were collected from each PWW. Maps showing water distribution areas of each PWW were obtained from municipalities. All the maps were digitized using CanMap 2.0 (Desktop Mapping Technologies, Markham, Ontario). CanMap data use the 1983 North American Datum (NAD 83) and contain streets, water bodies, and administrative boundaries. …