INDEPTH: WATER
Water Testing
CBC News Online | August 25, 2004
The May 2000 outbreak of tainted water in Walkerton, Ont. highlighted how vital it is to properly chlorinate water, test it for E. coli and to notify people immediately if water is contaminated. Laboratories across Canada conduct many tests on water to check if it is safe. Here's a look at how the scientists put their microscopes and Petri dishes to work.
What do water quality tests include?
Health Canada’s 1996 Guidelines for Canadian Drinking Water Quality includes guidelines for bacteria, protozoa, chemicals such as lead and nitrates, and radionucleotides.
What do the microbiological test results show?
Microbiologists look for the presence of two types of bacteria: total coliforms and E. coli. Total coliform bacteria are found in soil and the gut of humans and animals and may indicate fecal contamination. The Environmental Protection Agency compares coliform bacteria to police tape and chalk outlines that are often found at the scene of a crime – coliforms are associated with the crime of fecal contamination but are not criminals themselves.
E. coli have no non-fecal source, so if E. coli is found in water samples then it is definitely contaminated and is not safe to drink. The maximum acceptable concentration of E. coli is 0 per 100 mL of water.
Why can't labs just test for E. coli?
Until recently, water standards had to use coliform counts because it was difficult to distinguish the E. coli bacteria that indicate fecal contamination from the coliform bacteria. Part two of the Water Inquiry report recommends that the proposed Advisory Council on Standards consider replacing the total coliform test with an E. coli test, now that better tests are available to look at E. coli specifically.
What happens if a water sample tests positive for coliforms?
The drinking water guidelines state drinking water should not contain more than 10 total coliform bacteria per 100 mL of water. The presence of coliform bacteria in tap water suggests the treatment system is not working properly or there is a problem in the pipes.
If a sample contains coliforms then the water should be resampled. If the second sample also exceeds the limit then "corrective action should be taken immediately," such as repairing the disinfection/filtration equipment, flushing the pipes and protecting the source water to prevent contamination. Part Two of the Walkerton Inquiry Report summarized the Ontario standard: "In essence, the operator is to increase the chlorine dose until two successive samples show no bacteria."
When a sample tests positive for coliforms then it must also be analysed for fecal coliforms and E. coli. The EPA says a positive result to the last test represents a direct health risk and the public must be notified quickly.
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