Cistern Maintenance for Residential Settings

Some rural residents obtain their drinking water from a reservoir or cistern typically made from concrete.

A cistern is used most often in areas where wells do not provide sufficient water or have historically produced water that is unsuitable for drinking.

A properly constructed cistern filled with municipally treated water delivered by an approved water hauler should provide water that is safe to drink. However, a cistern still requires periodic inspection, cleaning, and disinfection. Poorly maintained cisterns are easily contaminated.


  • Use a cistern made from a material suitable for holding drinking water
  • Maintain the cistern in a manner that will prevent the entrance of bugs, rodents, and surface water runoff
  • Inspect the cistern annually for sediment, bio-film (slimy coating), debris, cracks and seepages, ill-fitting lids, and broken vent screens
  • Do not direct rainwater into the cistern. Bacteria from bird and animal droppings, dust, leaves, and chemical residues from roofing materials will contaminate the cistern
  • Refill the cistern with potable drinking water only. Potable water haulers typically obtain their water from a municipal water supply, and are inspected by Niagara Region Public Health. Ask your water hauler if they're inspected by Public Health, or contact Public Health at 905-688-8248, extension 7268 to ask if your water hauler is inspected


  • Empty and clean the inside of the cistern every one to two years. You can remove sediment and debris, check and repair any cracks or seepages, remove any bio-film, and repair any damage. A cistern that requires entry into it for maintenance and cleaning should be considered a confined space. Hazardous gases or low oxygen levels may be present. Only individuals trained in confined space entry should enter a cistern
  • Disinfect the cistern after cleaning


  1. Disinfect the cistern
    • After cleaning
    • If the cistern has become or may be contaminated
    • If a lab result indicates the cistern is contaminated
    • If an inspection reveals there is concern of contamination
  2. Add four ounces of household (5.25%) unscented bleach per 1,000 gallons of water
  3. Mix the bleach and water with a large clean object
  4. Run each water line (one at a time) in the house until a chlorine odour is noticed- that includes flushing all toilets, and running all baths and showers. If no odour is noticed, add a little more bleach to the cistern
  5. Let stand overnight (minimum 12 hour contact time required)
  6. After at least 3 days, submit a water sample for bacteria testing
  7. Do not drink the water (or use it for brushing teeth or washing fruits/vegetables) until you have received your test results. The water should be safe for bathing, showering, laundry, and toilet flushing
  8. It is recommended that at least a seven day supply of drinking water (bottled water) be arranged before starting this process (typically 1.5 litres per person per day should be enough)

Bacterial Testing

  • Free sample kits for bacteria testing are available from Municipal Service Centers and Public Health as listed on following page
  • Sample freshness and temperature control is essential for proper testing for bacteria. We recommend you take the sample on your way to the drop off site. If that is not possible then bring the sample to the drop-off location within 12 hours of collection and keep it cool in transit and in storage
  • Samples must reach the testing laboratory within 48 hours of collection time
  • If sample test results indicate the drinking water supply is unsafe, stop drinking it. It is recommended to inspect the cistern and resample and test the water. If the re-sample results indicate the water is unsafe for drinking and the cistern appears clean and maintained, disinfect the cistern according to the procedure above
  • Chronic unsafe test results indicate a likely need to install a permanent disinfection device such as a chlorinator or ultraviolet system. A professional should be consulted for assistance
  • Cisterns should be tested seasonally (spring, summer, fall and winter). If regular seasonal samples cannot be taken, then three samples, one to three weeks apart should be obtained. A single sample may not be representative of the quality of your cistern water. Continue to sample a minimum of four times per year. You can test more often if you want. The best time to sample cistern water is when the probability of contamination is greatest. This is likely to be in the early spring, after an extended dry spell, following heavy rains or after lengthy periods of non-use. In addition to regular tests, cistern water should be tested immediately after
    • Any repairs/replacement
    • The cistern has not been used for long periods of time (such as seasonal residences)
    • After flooding
    • There has been a change in the surrounding land use
    • There is any change in the water clarity, colour, odour or taste

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