Walkerton water worries keep the topic up front

by R.A. Clappison, DDS, FRCD(C)

With the number of deaths as high as 11, illness in the thousands and numerous business establishments seriously affected, nation-wide attention has been drawn to the problem of the safety of drinking water in this Ontario town of approximately 5,000 residents. The culprit was not the usual E. Coli but a lethal strain named Eshericha coli 0157:H7, an organism found in the digestive tracts of healthy cattle. The source is claimed to be contaminated surface water seeping into the town’s water source. Surveys of high density cattle presence has shown that areas with the highest number of cattle had the highest rates of E. Coli 0157 infection. High density farming found in “Feedlot Alley” in Alberta produces untreated waste from 1.3 million animals that equals human sewage from an urban population of eight million people.

In spite of not having any relationship to contaminated dental unit waterlines this tragedy can renew a topic patients may wish to discuss with their dentist or dental staff.

It is most reassuring to be able to inform a patient that your office follows the recommended guidelines that maintain adequate sanitation of your dental unit water lines. In addition, how effective it is to be able to accurately state that water samples are tested twice monthly by a reputable analytical laboratory and the data is promptly reported to you.

You or your staff member could quickly point out that:

1.The lines are flushed for at least two minutes (minimal).

2.100-mL of water is collected in a sterile sample vial.

3.Sodium thiosulphate is in the sample vial to counter the effects of the chlorine.

4.The samples are temporarily stored in the refrigerator and kept chilled during delivery to the laboratory by the use of freezer bags.

5.The laboratory then incubates the sample at 350C for 48 hours using an R 2A/spread plate method or on a Plate Count Agar/pour plate. They are both accurate.

6.The colonies are counted at 48 hours. Some laboratories read them again at 72 hours and some again at seven days. The results are promptly sent to the office and major problems are reported instantly. An unexpected high count can occur from a blob of biofilm coming loose and messing up your sample but that’s the way with biofilms.

Being a part of the above scenario endows you and your staff with a rightful sense of pride and satisfaction in that you are doing all you can to provide your patients with clean dental unit water. If you are not, this beneficial attitude can easily be attained by contacting analytical laboratories such as Micrylium; Microbex; E-3 Laboratory Services, Niagara-on-the-Lake, ON, other local analytical laboratories, your dental or medical faculty or your Ministry of Health.


1.Walkerton Becomes Premier’s Waterloo, National Post, June 9, 2000, Page A10

2.When Water Kills, Andrew Nikiforuk. Macleans, June 12, 2000, Page 21

3.An Evaluation of Sampling and Laboratory Procedures for Determination of Heterotrophic Plate Counts in Dental Unit Waterlines, Noce L., DiGiovanni D., Putnins E.E., EJCDA Website: www.cda-adc. Cda/j’cda/vol-66/issue-2/262-.html

4.Festin, Jane C. – Microbex Laboratories

5.Swift, Dean – Micrylium Laboratories

6.Oatley, Jason – E-3 Laboratories