Shocking a well

Shock chlorination is a relatively inexpensive and straightforward procedure used to control bacteria in wells.

Shock chlorination is the most effective way to eliminate harmful bacteria in wells.

What is shocking a well?

Shock chlorination is a relatively inexpensive and straightforward procedure used to control bacteria in wells. It involves adding a large amount of chlorine to the water in the well and pumping it through the water distribution system. The chlorinated water is left in the system long enough to ensure complete disinfection.

Why shock chlorinate a well?

Wells can become contaminated with harmful bacteria such as E. coli. Shock chlorination is the most effective way to eliminate these bacteria.

When should I shock chlorinate my well?

Wells should be shock chlorinated when a well water sample result shows that there is bacteria in the water. Any time a well is opened for repair it must be disinfected. Newly-built wells should also be shock chlorinated following construction.

How do I shock chlorinate my well?

You can easily shock your well by adding plain unscented household bleach with a chlorine concentration of 5 to 5.25%. The amount of household bleach used varies with the type of well you have.

Dug well (1 meter/3 foot diameter)

Add 1 litre (1 quart) of household bleach for every 1.5 metres (5 feet) of depth of water. If you don’t know how high the water stands, use the well casing depth to estimate how much household bleach to use.

Drilled well (15 centimeters/6 inch diameter casing)

Add 142 millilitres (5 ounces) of household bleach for every 7.5 metres (25 feet) of depth of water.

Well point (5 centimetres/2 inch diameter)

Add 85 millilitres (3 ounces) of household bleach for every 3 metres (10 feet) of depth of water.

Once you have calculated the correct amount of household bleach (chlorine):

Pour the bleach into the well. If possible, mix the water in the well. This can be done by attaching a hose to a tap, running water from the well, through the hose and back into the well.
Disconnect or bypass any carbon filters as these filters will remove the chlorine from the water, and any pipes beyond the filter will not get disinfected. If shocking due to unsatisfactory test results, consider replacing filters as they can harbor bacteria.
Run chlorinated water at every tap in the house until you smell a strong odor of bleach.
If there is no chlorine smell or it is very weak, add more bleach to the well and repeat Step 3.
Drain the water heater and fill with chlorinated water.
Backflush the water softener and all water filters.
Let the chlorinated water stand in the system for at least 12 hours.
Clear chlorine from the well by running an outside hose to the ground surface. Then run clear water through the faucets until the water no longer smells of chlorine.
Avoid putting too much chlorine into the septic system, too much chlorine may kill the bacteria needed for septic decomposition.
Reconnect any carbon filters (if the shock was due to unsatisfactory test results, replace with new carbon filters).
Wait at least 48 hours to take a water sample to ensure the water is safe to use.

Don’t drink the water without boiling it (a rapid rolling boil for at least 1 minute) until test results show that the water is safe to drink.

This item was last modified on June 2, 2022