We have been drinking our water at the cottage now for about four months with no problems. We just got back the test results saying “18 coliforms per 100 ml, no E. coli.” Is the water safe to drink?
Not according to Health Canada, the US Environmental Protection Agency and, chances are, your local public health office. Coliform bacteria occur naturally in soil and in the intestines of humans and animals. Any amount in your water could indicate that the water is contaminated by, for example, improperly treated septic and sewage discharge, or stormwater runoff. Since E. coli, on the other hand, is only found in the guts of mammals, if you’ve got it in your water, it suggests the water has been contaminated with fecal material.
No amount of E. coli is ever considered safe in drinking water (see above, re: fecal material), and Health Canada says that water with a total coliform count of less than 10 per 100 ml is only “marginally safe” to drink. A number higher than 10 is not safe. So you should really stop drinking your water and re-sample it. (You can, in the meantime, boil it before using it for drinking, washing food, brushing your teeth, or making ice cubes.) If you get the same results with a second water test, try to figure out if the contamination problem has a solution. If your water comes from a well, get your well inspected: Maybe surface water is getting inside and the well needs a repair. If your drinking water comes from the lake, you may need to install a water treatment system, or find another way to purify the water.
Can you drink water—even a lot of it—contaminated with coliform bacteria without getting sick? Sure. But you’re gambling with your innards. The presence of this bacteria means your water supply is vulnerable to other harmful micro-organisms. So, hey, better safe than a violent bout of gastroenteritis!