Water Quality

Drinking Water Treatment Process

Why do we need to treat water?

There are many impurities in the raw lake water that can harm human health if the water is ingested without treatment. These impurities can be grouped into three categories:

  • Physical: materials that do not dissolve in water and make the water appear "dirty".
  • Chemical: substances dissolved in the water from both natural and man-made processes.
  • Biological: viruses, bacteria, algae, and other small living organisms.

Is the drinking water that comes out of our tap "pure"?

"Chemically pure" water, entirely free from any other materials, does not exist in nature. An example of this form of water, distilled water, is usually flat and tasteless and few people enjoy drinking it. It would be prohibitively expensive and possibly unhealthy to purify our entire water supply to that level. "Natural water", free from any man-made additives (if it still exists) contains concentrations of minerals such as calcium, magnesium, and iron which are beneficial to human health in small quantities.

The purpose of the water treatment processes used by Toronto Water is to produce water that meets or betters all standards set for drinking water quality by the provincial and federal environmental ministries.

How does lake water get turned into drinking water?

View for a description of the drinking water process (PDF)

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