(Guide for Private Water Systems Only)
1. Draw off a small supply of drinking water for overnight use before disinfecting the well. See “Emergency Water Treatment” procedures for this overnight supply.
2. Determine the depth of your well. Mix the amount of liquid bleach, as described below, with several liters (10 to 20 litres) of water. Use common, unscented household bleach that does not contain detergent or other additives such as fabric-guard. Always follow the directions on the bottle label for safe storage, handling and use. Chlorine should always be used in well-ventilated places because breathing the fumes is dangerous.
The amount of chlorine required for a dug well ( 3′ diameter) is approximately 2 cups (500 mLs) of bleach per tile of water.
The amount of chlorine required for a drilled well (6″ diameter) is approximately 2 cups (500 mLs) of bleach per 50 feet of water.
Newly constructed wells may require stronger treatment (consult the well installer). Typically, new wells require a chlorine concentration of 250 mg/L or parts per million (ppm) whereas existing wells require 50 ppm chlorine for effective disinfection.
3. Remove the well cap and examine the well. Prior to adding the chlorine solution, the sides of the well should be cleaned – this is an optional process however it should make the overall disinfection of the well more effective. Consult with a licensed well technician / driller if you are unsure of how to proceed with cleaning to avoid damaging the well or well equipment.
In the case of large diameter wells such as dug wells, all floating debris should be removed and the casing/cribbing washed and scrubbed. Check to see that the tiles are sealed and that there are no leak stains where the tiles join together. Dug well tiles can be sealed with a suitable hydraulic cement – check with local plumbing and hardware stores. Scrub the sides of the well with a clean/new mop and chlorinated water. Remove all sludge that has accumulated at the bottom as bacteria will likely be present in the sludge. Since many bacteria are motile, meaning they have the ability to swim, they can escape the sludge and travel back and forth in a water column and in plumbing. In 5 – 6 “ drilled wells, pumping equipment would have to be removed before cleaning. After the cleaning the pump could be reinstalled and the well pumped until the water is clear.
4. Pour the mixed chlorine solution into the well. If the well is buried, either expose the top of the well, remove the well seal and pour the solution directly into the well, OR pour the solution through a clean funnel into the air vent or siphon through the vent (flush the air line with clean water after chlorination). Note: Wells should be above ground. If you have a buried well, consider adding an extension to raise the well 1 to 2 feet above ground.
5. If you have a carbon or charcoal filter, remove it from your system (after bleaching the system, replace with a new carbon or charcoal filter). If you have a water softener or other treatment equipment, check with your water treatment dealer about whether disinfection may adversely affect your treatment unit. It is possible for water treatment equipment to become fouled and lines into and away from equipment should be disinfected.
6. Start the pump and bleed air from the pressure tank.
7. Open one faucet in house and let the water run until you can smell the chlorine. Turn the faucet off. Repeat this procedure with all hot and cold faucets. This may take awhile for deep wells. Be sure to include all inside and outside faucets, cold and hot water, dishwashers, toilets, baths, showers etc. The principle is to have disinfectant in every plumbing line in the house as well as disinfectant in the well.
Chlorine is a very reactive substance. When added to the well it will first combine with organic and inorganic substances such as iron, hydrogen sulfide and algae. There is no disinfection at this point. After the demand of these compounds has been met, then the residual chlorine begins the disinfection process. If there is no smell of chlorine coming through or the smell is faint, then more chlorine may have to be added to the well to achieve adequate disinfection.
If you are having trouble getting the chlorine down to the pump level, hook one end of a garden hose to an outside tap and insert the other end into the top of the well. Turn on the outside tap until you smell the bleach coming through the other end. This helps to re-circulate the water and drive the chlorine down to the pump. Once you smell the chlorine coming from the garden hose, shut off the outside tap and proceed with opening all of the taps, hot and cold, in the house. Turn off the taps once you smell the bleach coming through.
8. Seal the top of the well. Let the system sit for a minimum of 6 hours or preferably overnight. Do not leave chlorine in the system for more than 24 hours as it may affect some pump parts.
9. After the 6 to 12 hours, flush the well using an outside tap until the chlorine odor has completely disappeared. (Using an outside tap prevents a large amount of bleach from entering the septic tank that could kill the good bacteria working in the tank). Afterwards, flush the lines of the house also.
Note: As chlorine comes in contact with dissolved iron in water, the iron will precipitate out as rust and the water will turn a yellow color. Other staining and sedimentation problems may occur. If this is the case with your water, remove the screens from the faucets before flushing the lines. This problem should clear up with time and flushing. It may take a few days. In the meantime, do not use this water for aquariums or pets. Check with your physician about other uses of the water, such as bathing, if you have allergies or other medical concerns.
Note: Do not flush the water into a natural body such as a lake, stream or creek; avoid flushing into gardens.
10. Wait one to five days before collecting a sample for bacteriological testing. There should be no chlorine odor remaining at the time of sampling. Boil or chlorinate all drinking water, or use an alternate source, until you receive a satisfactory laboratory report.
11. If the results come back with NO detectable bacteria then:
a) After one to two weeks, sample again to ensure that the well is not recharging with contaminated water. Two consecutive “safe” tests, performed on samples obtained over a period of one to three weeks, will probably indicate that the treatment has been effective.
b) Sample regularly 2 to 4 times a year to ensure the water supply has remained secure.
Note: In Ontario, samples can be submitted to the local Public Health Unit for testing of bacteria at little or no charge for private residents; verify with your local Health Unit.
If the results come back WITH bacteria then
Contact a licensed well technician to inspect your water system.
If the source of contamination cannot be found and eliminated, the water should subsequently receive continuous disinfection.