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Water Safety

How to Clean and Disinfect a Cistern

​​Cisterns are watertight containers to protect and store drinking water. In some circumstances, the water from a cistern may not be safe to drink.

If cistern collars, lids, fill ports, or screened vents are damaged, germs (contaminants) may get in. If the cistern structure is damaged (e.g., frost, settling), cracking below the surface may happen, which could let contaminated groundwater and soil in. Cisterns in areas at risk for floods may also be at risk of overland flooding from surface water. If you see any areas that germs could get in or your test results show the water is contaminated, it’s important to fix the problem.

Once the contamination problem is fixed, follow the steps below to clean and disinfect your cistern. You’ll need to arrange to have an approved water hauler on-site before this. You need clean, safe water to clean and disinfect a cistern.

​When do I need to test my cistern for bacteria?

The Provincial Laboratory for Public Health (ProvLab) tests private water drinking water systems for bacteria. However, the ProvLab can’t test water for every type of harmful germ.

The ProvLab does 2 standard tests (total coliforms, E.coli) on water samples. These results will show how likely the water is to be contaminated with bacteria. Coliforms are a group of bacteria that are found everywhere (e.g., soil, on plants, lake and river water). People and animals have E. coli bacteria in their bowels and stool.

Test your cistern:

  • 2 times a year for routine monitoring (e.g., in the spring, in the fall)
  • whenever there are changes to the water quality (e.g., water clarity, colour, smell, taste). Check the inside of the cistern and ask your bulk water hauler if there have been any changes to the source water supply.
  • when it’s been disinfected (to make sure it worked)

If you know the water is contaminated (e.g., you see rodents in the cistern), clean and disinfect it right away. You don’t need to test the water first.

Current as of: December 22, 2014

Author: Environmental Public Health, Alberta Health Services