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Water Safety

How to clean and disinfect a cistern

​​​​​​​​​​​​​​​​​​​​​​​​​​Cisterns are watertight containers to protect and store drinking water. But sometimes the water from a cistern may not be safe to drink. If this happens, you need to fix the problem and then clean and disinfect the cistern so it’s safe to use again.

How could water in a cistern become contaminated?

The following problems could allow germs to get into a cistern and contaminate the water:

  • damage to cistern parts such as collars, lids, fill ports, or screened vents
  • damage to the structure
  • overland flooding

After you know the problem, you need to fix it before you clean and disinfect the cistern.

When do I need to test my water?

It’s recommended to test the water in a cistern at the following times:

  • 2 times a year for routine monitoring (such as 1 time in the spring and 1 time in the fall)
  • whenever the water quality changes (for example, it looks, smells, or tastes different than usual)
  • right after the cistern has been disinfected

If you know the water is contaminated—for example, you see rodents in the cistern—clean and disinfect it right away. You don’t need to test the water first.

​Who tests drinking water and what do they test for?

The Provincial Laboratory for Public Health tests private drinking-water systems for bacteria. The lab can’t test water for every type of harmful germ, but they test for 2 common types of bacteria that could make you sick:

  • Total coliforms are a group of bacteria found naturally in soil, on plants, and in lake and river water.
  • E. coli bacteria are found in the bowels and stool (feces) of people and animals
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Current as of: May 25, 2022

Author: Environmental Public Health, Alberta Health Services