Manitoba Water Well Association

1082 Main Street, Winnipeg, Manitoba R2W 5J3

Phone: 204.589.6166

Email: mwwa@mwwa.ca

Resources:

How Do I Disinfect My Well?
While Manitoba has an abundance of good quality water,
private wells can become contaminated with bacteria. The
risk for bacterial presence in well water is increased by
factors or conditions such as:
• Groundwater sources which may be open to the
surface because of shallowness and/or water
permeable overlying soils such as sand and gravel.
These include sources covered by less than six meters
of glacial till, clay, clayey shale or other non-watertight materials;
• Wells which are located in pits or depressions;
• Wells with unsealed casings, casings that do not
extend at least 30 cm or more above the ground, or
casings that are rusted out in spots;
• Wells near abandoned wells which have not been
sealed;
• Wells within 30 meters of septic tanks or fields, barns,
feed lots, sink holes, or quarries;
• Wells or groundwater sources affected by changes in
environmental conditions such as floods or heavy
rains, or an extended dry spell.
If any of these situations exist they should be corrected
where possible.
As a general practice, well disinfection should be used to
ensure the water is bacteriologically safe anytime a new
well is installed, well or pump service is performed or
bacteriological tests indicate a problem.
The following procedures describe two different methods
for proper disinfection of the well and distribution system.
If a properly sized storage tank is available, a full
chlorination procedure is always recommended. If the
properly sized storage tank is not available, a partial
chlorination of the well may be acceptable. Both chlorination
procedures should be followed by bacteriological testing at
least one week after the disinfection process.
Caution
• If your well is a pit type, do not enter without
following confined entry practices. For more
information on confined entry practices contact
Workplace Safety and Health at 945-3446.
• Be careful when handling chlorine/bleach and use
proper safety procedures - wear protective eyewear,
gloves, and clothing.
• Numerous chlorine products are now available with
additives for various cleaning applications. These
should not be used. Also, chlorine content may vary
from product to product. All application rates used
in this document are based on 5.25 percent available
chorine (regular household bleach). Check the
product label to be sure.
Full shock Chlorination
• Store enough water to last the household for 24 hours.
Pump 1500-2500 litres of water into a clean container
located near the head of the well. Use only containers
that have been used to hold drinking water.
Containers that have been used to hold petroleum
products, pesticides or fertilizers should not be used.
• Pour ten litres of regular household bleach (5.25%
sodium hypochlorite) into the container and an
additional ten litres into the well.
• Rinse down the sides of the well casing with a garden
hose for five to ten minutes. Make sure the hose is
connected to the system being chlorinated. This
procedure circulates the chlorine solution throughout
the water system to ensure total disinfection.
Well WaterFact Sheet
Office of the Chief Medical Officer of Health
March 2001
• Let stand for one hour to allow the added chlorine to
mix with the entire water column within the well.
• Siphon or pour the 1500-2500 litre mixture of water
and chlorine into the well casing. (regulate the flow to
prevent the well casing from overflowing)
To disinfect your household plumbing system, you can
turn on each of your water taps until the chlorine smell is
just detected and then turn them off. Water treatment
equipment should be bypassed during this process. Shut
power off to your water heater while carrying out a
household disinfection process. Let the chlorine solution
remain in the system for at least 12 hours, but preferably
for 24 hours. After this period, pump all of the chlorine
solution out of the well by attaching a garden hose and
running the water to an area away from grass and
shrubbery where the chlorine will do no damage.
(Chlorine can kill fish and aquatic organisms so make
certain that the chlorine does not enter any watercourse.)
• Do not dump the spent chlorine solution into your
private septic system as it will kill bacteria essential
for the proper operation of your septic tank and field.
• Pump until you can no longer detect the chlorine smell.
• Do not run water through your household system
until well water is clear.
• Follow this procedure for your plumbing system by
running each of the cold water taps.
• Drain down water heater, refill and turn power back on.
• Resample well for bacteriological contamination no
sooner than one week after disinfection procedure.
Partial Chlorination
Determine the minimum amount of chlorine required (see
below) needed to achieve effective disinfection of the well.
Table 1
Disinfection of Well Water with Regular Household
Bleach (5.25% sodium hypochlorite)
Remove the cap from the well and pour half of the
determined amount of chlorine bleach into the well. Rinse
down the sides of the well casing with a garden hose.
Make sure the hose is connected to the system being
chlorinated. Insert the running hose into the top of the
well far enough to be sure that it will stay secure while
disinfecting the plumbing system. Letting the hose run
circulates the chlorine throughout the water column to
ensure total disinfection.
To disinfect your household plumbing system, turn on
each of your water taps until the chlorine smell is just
detected and then turn them off. Water treatment
equipment should be bypassed and, shut off power to your
water heater while carrying out the disinfection process.
Once the household plumbing has been disinfected as
described in the previous section, pour the remaining
bleach into the well, again rinsing off the well casing with
the hose. Allow the hose to run for an additional 10 to 15
minutes. Replace the cap on well and let the solution
remain in the system for at least 12 hours, but preferably
for 24 hours.
After this period, pump all of the chlorine solution out of
the well by attaching a garden hose and running the water
to an area away from grass and shrubbery where the
chlorine will do no damage. (Chlorine can kill fish and
aquatic organisms so make certain that the chlorine does
not enter any watercourse.)
• Do not dump the spent chlorine solution into your
private septic system as it will kill bacteria essential
for the proper operation of your septic tank and field.
• Pump until you can no longer detect the chlorine smell.
• Do not run water through your household system
until well water is clear.
• Follow this procedure for your plumbing system by
running each of the cold water taps.
• Drain down water heater, refill and turn power back on.
• Retest well for bacteriological contamination no
sooner than one week after disinfection procedure. Diameter of  Chlorine bleach  Chlorine bleach added
Well Casing added per Meter per 3 Meters (10 feet)
2 inch (5 cm.) 10 ml 30 ml.
4 inch (10 cm.) 40 ml. 120 ml.
6 inch (15 cm.) 90 ml. 1/4 Litre
8 inch (20 cm.) 160 ml. 1/2 Litre
30 inch (75 cm.) 2 1/4 Litres 6 1/2 Litres
36 inch (90 cm.) 3 1/4 Litres 9 1/2 Litres
Drinking Water Fact Sheets
How Do I Know If My Well Water Is Safe from
bacterial contamination?
How Do I Test My Well Water for bacterial
contamination?
What Do I Do When a Boil Water Advisory is
Issued?
How Do I Disinfect My Well?
Guidelines for Food Establishments
During a Boil Water Advisory
Where can I get more information?
For further information on well water safety, please
contact the nearest office of Manitoba Conservation or
The Manitoba Water Services Board at the numbers
listed on this fact sheet, or call Health Links at 788-8200
or toll-free 1-888-315-9257.
Manitoba Conservation
Winnipeg 204-945-0675
Fax 204-945-1211
Brandon 204-726-6064
Fax 204-726-6567
Virden 204-748-2321
Fax 204-748-2388
Steinbach 204-346-6060
Fax 204-326-2472
Selkirk 204-785-5030
Fax 204-785-5024
Lac du Bonnet  204-345-1447
Fax 204-345-1415
Flin Flon 204-687-1625
Fax 204-687-1623
The Pas 204-627-8307
Fax 204-623-1773
Killarney 204-523-5285
Fax 204-523-4626
Dauphin 204-622-2030
Fax 204-622-2306
Swan River 204-734-3436
Fax 204-734-5151
Winkler 204-325-1750
Fax 204-325-1758
Portage
la Prairie  204-239-3188
Fax 204-239-3185
Thompson 204-677-6704
Fax 204-677-6652
The Manitoba Water Services Board
Brandon 204-726-6079
Fax 204-726-6290
Dauphin 204-622-2116
Fax 204-622-2298
Beausejour 204-268-6059
Fax 204-268-6060
Office of the Chief Medical Officer of Health
4th Floor, 300 Carlton Street
Winnipeg, MB R3B 3M9
Ph: (204) 788-6666
Fax: (204) 948-2204
Information Compiled by the Drinking Water
Coordinating Group

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