Disinfection is routinely used to control bacteria in water wells and is applied as part of a start-up procedure for newly constructed wells and should be used as semi-annual maintenance for existing wells. Disinfection should also be performed in the event of contamination. Well disinfection can be performed by two methods low and high level disinfection. High level disinfection is the preferred option. However, if proper equipment (e.g. 1360 litres [300 gallons] tank) is not available then low level disinfection, as described in this fact sheet, may be adequate.

Until the disinfection procedure has eliminated a bacterial contamination, an alternate source of safe water should be used or the water boiled for 1 minute, at a rolling boil, before use. In addition, if possible identify and eliminate the source of contamination.

Disinfection can be conducted using unscented household bleach. Check the product label to ensure that the chlorine is in the form of sodium hypochlorite or calcium hypochlorite. Some "all purpose bleaches" (such as Javex 2) contain no chlorine and should not be used for disinfecting wells.

Table 1 below outlines the quantity of bleach required to properly disinfect a well.

1. Follow chlorine manufacturer’s instructions for use. Chlorine concentrations at this level are dangerous. Avoid contact with skin, inhaling the fumes and wear protective clothing/eye wear. If your well is located in a pit, you must make sure there is proper ventilation during the chlorination procedure. It is recommended that you contract the services of a licensed well driller who has the proper equipment and experience to do the job safely.
2. Ventilate confined spaces, e.g., well pit, crawl space, and all other confined spaces where potentially dangerous levels of vapours may accumulate.
3. Do not run chlorinated water through certain types of water treatment equipment (e.g., softeners, carbon filters, reverse osmosis systems). For specific information, contact your equipment dealer or the Saskatchewan Watershed Authority.
4. If a well is slow yielding or tends to pump any sediment, be careful when you chlorinate. Slowly siphon the solution down the well and pump it out very slowly. Over pumping the well may worsen the sediment problem.
5. The disinfection treatment will require the well to be taken out of service. Therefore, store sufficient water to meet all necessary requirements for a minimum 12 to 24 hour period.
6. Add the amount of unscented bleach indicated in Table 1 below directly into the well. Connect a garden hose to a nearby tap and wash down the inside wall of the well. This will ensure thorough mixing of the chlorine and the water throughout the well.
7. Start the pump and bleed air from the pressure tank. Open each tap and allow the water to run through all taps until a smell of chlorine is detected, then turn off the taps. If a strong smell is not detected, add more bleach to the well and repeat step 7.
8. Allow the water to sit in the system for 12 to 24 hours.
9. Start the pump and run water through an outside hose away from grass, shrubs, trees and other sensitive plants until the strong smell of chlorine disappears. Make certain that the water does not enter any watercourse. Finally, open the indoor taps until the system is completely flushed. Return the system to normal operation.
10. If low level disinfection is being used to eliminate a bacterial problem, verify that the procedure has removed the bacteria by following the steps under Disinfection Verification.

Table 1. Disinfection of Well Water with Unscented Household Bleach
(Approximately 5.2% Hypochlorite)

Until water testing indicates that the water is safe to use, find another source of water, or boil the water for one minute, at a rolling boil, before consuming. This precaution is particularly important for persons who are immunocompromised and also if the water is being used for infant feeding (preparing formula, etc.).

For private water supplies, it is recommended that a sample be taken 5 days after treatment and another at least one week after constant use. Two consecutive ‘safe’ test results are required to ensure that the treatment was effective.

For Health regulated public water supplies:

• wells not receiving continuous treatment require a sample taken 5 days after treatment and another at least one week after constant use;
• wells receiving continuous disinfection treatment require at least 2 consecutive sets of samples. The samples should be taken at least one day after the treatment and one day apart. Health Region officials will be advising the owner/operator of the supply on number of samples, sampling locations and as to when the water supply can be used again for human consumption.

In general, all private systems should be analysed at least once a year or whenever there is reason to believe that the water supply may have become contaminated (e.g. flooding).

Health regulated public water supplies must sample as required by the health region.