Here is how to disinfect a well with shock chlorination, which kills the bacteria in your well and in your home’s plumbing. Pure H2O’s procedure has 8 steps, with a calculator that tells you how much bleach to use. Plan for 24 hours without using the water.
Download the printable procedure (PDF, in French)
When should you disinfect your well?
- Your water test shows coliforms, E. coli or enterococci.
- After work on the well or the pump.
- After a flood near the well.
- For a new well (the dose is stronger: see the calculator).
Before you start
What you need
- Gloves and safety glasses
- 5% household bleach: fresh, unscented and with no additives (never pool or spa products)
- A bucket of about 20 litres (5 gallons)
- A garden hose long enough to reach the well
- A skimmer net, for a dug well
- A supply of drinking water for at least 24 hours
Safety first
- Turn off the power to the pump at the electrical panel before opening the well.
- Keep the area well ventilated and never mix bleach with another product.
- Put your water treatment equipment on bypass: softener, filters, reverse osmosis. Concentrated chlorine can damage it.
How much bleach do you need to disinfect a well?
Enter your well’s details: the calculator gives the amount of 5% bleach to use.
Total depth minus the water level (see your well drilling report). Not sure? Enter the total depth.
Another diameter? Call us at 1-888-840-0558.
Prefer the tables? Here are the same amounts.
| Height of water | 6 in. casing | 8 in. casing |
|---|---|---|
| 50 ft (15 m) | 300 mL | 500 mL |
| 100 ft (30 m) | 600 mL | 1 L |
| 150 ft (46 m) | 900 mL | 1.5 L |
| 200 ft (61 m) | 1.2 L | 2 L |
| 300 ft (91 m) | 1.8 L | 3 L |
| Height of water | 36 in. | 48 in. |
|---|---|---|
| 5 ft (1.5 m) | 1 L | 1.8 L |
| 10 ft (3 m) | 2 L | 3.6 L |
| 15 ft (4.6 m) | 3 L | 5.3 L |
| 20 ft (6.1 m) | 4 L | 7.1 L |
New well: multiply the amount by 5.
8 steps to disinfect a well
1. Turn off the power and open the well
Turn off the power to the pump at the electrical panel. Remove the well cap, then clear out leaves, debris and visible deposits.
2. Dilute and pour the bleach
Mix the amount given by the calculator in a bucket of clean water (about 20 litres), then pour the mixture into the well.
3. Circulate the chlorinated water for 1 hour
Turn the pump’s power back on, without touching the wires. Connect the hose to an outdoor tap (or to the tap on the pressure tank) and put the other end in the well. Open the tap: the water circulates in a loop. As soon as it smells of chlorine, rinse the inside walls of the well with the spray, then let it circulate for 1 hour.
4. Close the well
Close the tap, remove the hose and put the well cap back on.
5. Disinfect the plumbing
Make sure your treatment equipment is on bypass. Open each cold water tap one at a time, indoors and outdoors, starting with the farthest one. Close it as soon as the water smells of chlorine. Then do the same with the hot water, including showers and toilets.
Soak the tap aerators in chlorinated water (5 mL of bleach per litre of water).
6. Let it work for 24 hours
Close the main water valve and do not use the water for 24 hours: not for drinking, cooking or washing.
7. Flush out the chlorinated water
Reopen the valve. Start outdoors: connect the hose to an outdoor tap, run it to a drainage ditch away from the well, plants and waterways, and let it run until the chlorine smell is gone. Then run each indoor tap, put your treatment equipment back in service and reinstall the aerators.
Caution: do not empty the well all at once. Go gradually, with breaks if your well has a low flow rate.
8. Have the water tested
Have the water tested by an accredited laboratory one week after the disinfection, then again four weeks later. You can order a water potability test kit online. Until you get a satisfactory result, boil the water for at least 1 minute before drinking it.
Prevention
- Have your well water tested at least twice a year, in spring and fall, as recommended by Quebec’s Ministry of the Environment (in French).
- If bacteria come back, do not repeat the disinfection more than once: the cause has to be found (a poorly sealed well cap, surface water seeping in, a faulty septic system). A UV system (store page in French) can then protect your water continuously.
Need help?
- You have a recent water test: send it to us and we will tell you whether a disinfection is enough.
- You have no water test: order a potability test kit online or call us.
- You want a permanent solution: book an appointment for a quote and the installation of a UV system.
Phone: 1-888-840-0558 · Email: info@ecopureh2o.com · Contact us
Source: Health Canada, Well water and health: Treat your well water.
