As we so well know from the Walkerton experience, municipal and rural water supplies can become contaminated. Municipalities do have testing mechanisms in place. And although they were not applied in Walkerton, because of that experience we can probably feel even more confident that municipal water supplies are safe. Still, it is possible for other contaminants to enter the system after the water leaves the water treatment plant. Notably, lead from your own plumbing, or bacteria from your own poorly maintained filter system.
But the water that homeowners and cottage owners have to be the most careful of is well water. Noone else is there to test it for you. You should be testing once a year for total coliform and E. coli indicator bacteria. If you have a bacteria problem, one of those two will be present. Municipalities throughout the country will do those tests for you for free. Contact your local health department to find out how to obtain the instructions and sample bottles. Follow the instructions to the letter. If the report comes back with danger signs, conduct three tests about a week or so apart to determine whether there is a real problem, or whether the sample was simply contaminated or did not get to the lab within the proper time limit.
You can purchase DIY test kits that will give you the same results without having to run samples into the health department, but you will have to pay for these.
To test for other things, like insecticides and chloroform and lead, you will either have to purchase specific DIY kits, or pay to have a water testing laboratory do the tests for you.
For more information you can contact Health Canada or Environment Canada, or if you want to test your own water call your local health unit or your provincial Ministry of Health. Check the blue pages of your phone book.
The water testing kits are available in Canada at ACE Hardware affiliated stores.