Cistern Maintenance & Water Testing

Some rural residents get their drinking water from a reservoir or cistern typically made from concrete. A cistern is used most often in areas where wells do not yield enough water or have historically produced water that is unsuitable for drinking due to taste, odour and/or mineral characteristics. 

A properly constructed cistern or filled with City of Hamilton water delivered by an water hauler approved by the City should provide water that is safe to drink but a cistern requires periodic inspection, cleaning and disinfection. Poorly maintained cisterns are easily contaminated. Cistern owners are responsible for the condition of their cistern and proper maintenance.

Maintaining your cistern

A cistern should be tightly sealed and constructed from material suitable for holding drinking water. You need to:

• Maintain the cistern to prevent bugs, rodents and surface water runoff from getting in.
• Inspect the cistern from the outside every year for sediment, debris, wildlife, cracks, ill-fitting lids and broken vent screens. Repair and clean as necessary.
• Refill the cistern with potable drinking water only. Potable water haulers typically get their water from a municipal water supply and are inspected by Public Health Services. Call Public Health at 905-546-2189 to ask if they inspect your water hauler.

Do not direct rainwater into the cistern. Bacteria from bird and animal droppings, dust, leaves and chemical residue from roofing materials in the rainwater will contaminate the cistern.

Cleaning your cistern

We recommend that you have at least a two to three day supply of bottled drinking water before cleaning and disinfecting your cistern. Typically 1.5 litres per person per day is enough water.

Empty and clean the inside of your cistern every two to three years to remove sediment and debris. A cistern that requires you to go into it for maintenance and cleaning should be considered a confined space. There may be hazardous gases or low oxygen levels in the cistern. Only people trained in confined space entry should go into a cistern.

Disinfect the cistern after cleaning using the following steps:

1. Ensure the cistern is clean and properly maintained - dirt and sediment is removed and holes are fixed.
2. Add four ounces of household unscented bleach (5.25%) per 1,000 gallons of water.
3. Mix the bleach and water with a large clean object.
4. Run each tap one at a time in the house until you notice a chlorine odour. If you do not notice an odour, add a little more bleach to the cistern.
5. Leave the bleach and water mixture in the cistern overnight, or for a minimum of 12 hours.
6. After the required contact time of 12 hours take a water sample and it drop off for bacteria testing.
7. Do not drink the water, use water for brushing teeth or washing fruits or vegetables until you receive your test results. You can use the water for bathing, showering, laundry and flushing the toilet.

Testing water from private cisterns is the responsibility of each property owner. To ensure your cistern water is safe to drink, we recommend testing your cistern water at least four times each year for bacteria.

The Ministry of Health and Long Term Care provides free water testing for bacteria, including E.coli and total coliform, from private cisterns.

Water test results

You will get your well water test results by mail if you completed the form in the testing kit or you can follow instructions on the blue card enclosed with your testing kit to get test results from the automated telephone system.

• How to interpret drinking water test results

If test results indicate the water is unsafe to drink, do not use the cistern water for drinking.  Inspect the cistern and re-test the water. If the test results indicate the water is unsafe for drinking but the cistern appears clean and maintained, disinfect the cistern.

Repeated test results that indicate the water is unsafe to drink may mean you need to install a permanent disinfection device such as a chlorinator or ultraviolet system.