Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs
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The Quality of My Well Water

Water is a resource that is both invaluable and vital. As the owner of an individual well or waterworks system serving less than 21 persons, you are responsible for ensuring its quality with a view to protecting your health and that of your loved ones. In this document, you will find all the information you need to meet this obligation.

Other Document

I get my well water tested! (Information sheet - PDF, 414 KB)

List of accredited laboratories (French)

The quality of my well water and my responsibilities

Whether water that is intended for consumption comes from a surface well or a cased well (commonly known as an "artesian well"), it must be of good quality and meet the standards set out in the Regulation respecting the quality of drinking water (Q-2, r.40). Under section 3 of the regulation, owners must provide their families and visitors with safe drinking water.

While well water may appear to be clear and pure, and have no specific odor or taste, it may contain elements that can have undesirable effects on health, for example pathogenic micro-organisms (bacteria, viruses, or protozoa) and nitrates/nitrites.

Groundwater, which is generally of better quality than surface water (lakes, rivers, streams) owing to the soil’s natural filtering capacity, may be vulnerable to contamination, and precautions must be taken to ensure a supply of good quality water at all times.

A contamination event can occur sporadically and the only way it can be detected is by analyzing the water. The Ministère therefore recommends that you have your water analyzed by an accredited laboratory:

Additional tests should be performed if you notice sudden changes in the water’s taste, odor, or appearance or if changes have been made to the well or surrounding soil.

Microbiological parameters

  • E. coli bacteria
  • Enterococcal bacteria
  • Total coliform bacteria

Physico-chemical parameters

  • Arsenic
  • Manganese
  • Barium
  • Nitrates-nitrites
  • Chlorides
  • Sodium
  • Iron
  • Sulfates
  • Fluorides
  • Total hardness based on the calcium and magnesium content

Water analysis alone is not enough to guarantee the quality of your drinking water. In addition to the recommended analyses, you must regularly check the condition of your well and septic facilities, examine possible sources of contamination in the well’s environment and make the appropriate corrections.


Microbiological indicators of water quality

The majority of pathogenic micro-organisms (potentially disease-causing viruses, bacteria or protozoa) that are likely to be found in water come from human and animal excrements. As it is technically impossible to analyze all pathogens, we use microbiological indicators that in themselves are harmless: E. coli bacteria, enterococcal bacteria, and total coliform bacteria.

E. coli bacteria are very abundant in the bowel flora of humans and animals, and this is the only species that is strictly fecal in origin. E. coli bacteria are considered to be the best indicator of fecal contamination. Their presence in water means that it has been contaminated by pollution of fecal origin and that it may contain pathogenic microorganisms.

Gastroenteritis is the illness most commonly associated with drinking water contaminated with fecal matter. While this disease is often minor, it may occasionally have very serious consequences on a person’s health. Other rarer diseases such as hepatitis or meningitis may also result from the ingestion of contaminated water. This risk concerns not only the members of a family who drink well water, but also all their visitors.

Enterococcal bacteria are less abundant in the bowel flora of humans and animals than E. coli bacteria, and some species are not of fecal origin. The detection of enterococcal bacteria in well water may indicate fecal contamination or infiltration of surface water. However, it is best to play it safe and consider the presence of enterococcal bacteria as an indicator of fecal contamination.

Total coliforms form a heterogeneous group of bacteria of fecal and environmental origin. Indeed, most of the species may be naturally occurring in the soil and in vegetation. Their presence in water does not generally indicate fecal contamination or a health risk, but rather a deterioration of the bacterial quality of the water. This deterioration may be attributed among other things to the infiltration of surface water in the well, or the gradual growth of a layer of bacteria on the walls, called a biofilm. The analysis of total coliforms makes it possible to obtain information on the potential vulnerability of a well to surface pollution.


Presence of E. coli or enterococcal bacteria in my water

Drinking water must be free of any trace of E. coli or enterococcal bacteria. When either type of bacteria is detected, it is essential that you boil the water for at least one minute before consuming it, obtain drinking water from a public water system, or buy bottled water. You must also use boiled water to make ice cubes, prepare drinks and food for babies, wash food that will be eaten raw, and brush your teeth. You can continue using the well water to shower or bathe (being careful to avoid swallowing it), but you should give children and babies a sponge bath. These recommendations must be followed until subsequent tests show that the water complies with applicable standards.

It is recommended that you determine the source of fecal contamination and take the appropriate remedial measures, if possible. A shock treatment to disinfect the well may be necessary, particularly if the contamination is caused by special circumstances (a thaw, abundant rain, etc.). Since shock treatment can damage water treatment equipment, it is recommended that you disconnect your equipment, if this applies, before starting the procedure.

Take the following steps to disinfect a well:

  1. Clean the well with a net, if possible, to remove foreign objects, deposits, animal or plant material, etc.
  2. Pour bleach into the well according to the quantities mentioned in the following table entitled “Quantity of Bleach Required for Disinfecting a Well.”
  3. Mix the bleach with the well water and, where possible, wash and brush the sides clean. You can also hook up a hose to the nearest tap and rinse the sides of the well to ensure complete mixing of the chlorine and water in the well.
  4. Turn all cold water taps on. When you detect the smell of chlorine, stop the pump and turn the taps off.
  5. Wait 24 hours before turning the water back on.
  6. Purge the system by letting the water run for an extended period of time until the smell of chlorine disappears. Turn all the taps on to rinse the pipes thoroughly. However, it is not necessary to purge your water heater.
  7. Test the water again one week and four weeks after disinfection to find out if the water complies with quality standards.


Presence of total coliforms in my water

The presence of total coliforms makes it even more important to conduct regular tests and take appropriate remedial measures to prevent any eventual fecal contamination. If new tests confirm the presence of total coliforms in concentrations exceeding the standards (above 10 ufc/100 ml), it is recommended that you give the well a shock treatment (disinfection).

Determining the source of contamination

It is important to identify the source of contamination and take appropriate remedial measures to improve the long-term quality of the water. There may be many local sources of contamination:

  • A well in poor condition (cover or sealant are not watertight, deteriorated materials, etc.)
  • Inadequate slope around the well (no mound around the well to keep away surface runoff)
  • Defective septic facilities
  • Unsanitary premises (e.g., manure spreading or other activities generating fecal matter nearby

In such cases, work should be undertaken to correct the situation or bring it to the attention of the person responsible for the source of contamination. Anyone confronted with a contamination problem can get in touch with the appropriate municipal official, who will help find a solution. Additional water tests should be done to check if the measures taken were effective.  

The quality of my well water during a flood

Owners of private wells must take special precautions during floods, as such events can pose serious risks for the quality of groundwater, which can be contaminated by river water or septic facilities nearby. To prevent risk of illnesses related to drinking contaminated water, the Ministère recommends the following measures:

  • During the flood: water from any well in the flooded area should be considered to be unfit for drinking. In such cases, you should obtain drinking water from another source (e.g., a public water system or bottled water) or boil any water intended for drinking or preparing raw food for one minute.
  • After the flood: after the floodwaters have completely subsided, owners should first check the well equipment, especially the electrical circuits. They should then wait a minimum of ten days before disinfecting the well according to the procedure described in a previous section and ensure that the results of both series of recommended water tests are in compliance before drinking the water again.


Quantity of bleach required for disinfect a well

It is recommended that you use 50 mg/l of free chlorine to disinfect an existing well (use 5% fragrance free bleach available in stores). To disinfect a new well, multiply the amount of bleach by five as the recommended concentration is 250 mg/l of free chlorine.

The tables below will help you determine the quantity to use according to the diameter and depth of your well.

Quantity of chlorine bleach needed to disinfect a well

Recommendations call for a concentration of 50 mg/l of free chlorine in order to ensure the efficient disinfection of an existing well (use 5% unscented, recently purchased, commercially available chlorine bleach). To disinfect a new well, multiply the bleach volumes shown in the following tables by 5, since a concentration of 250 mg/l of free chlorine is recommended in this case.

The following tables can be used to determine the required quantities on the basis of the diameter and height of the water column.

Height of the well water column

The height of the well water column is the depth of the well less the depth of the water. As an example, for a well whose depth is 180 ft. and where water depth is 30 ft., the height of the water column would be 150 ft. (180-30).

For shallow wells, the depth of the well and the water can be easily measured to precisely determine the height of the water column. A very clean measuring tape is required.

For tube or artesian wells, the information can be found in the drilling report. If no water depth information is available, the depth of the well should be used as the height of the water column. If you do not know the depth of the well, you should contact the municipality, where the information is normally on file, or check the Ministère hydrogeological information system or send an email to

Quantity required for a surface well

Surface wells are generally made of superimposed concrete pipes over 600 millimeters in diameter. They are rarely more than 9 meters deep.

Surface Well

Height of the well water column (metres)

Well diameter








Millilitres of bleach


700 ml

1 000 ml

1 300 ml

1 600 ml

2 000 ml

2 300 ml

2 600 ml

1 067

900 ml

1 400 ml

1 800 ml

2 200 ml

2 700 ml

3 100 ml

3 600 ml

1 219

1 200 ml

1 800 ml

2 300 ml

2 900 ml

3 500 ml

4 000 ml

4 700 ml

1 372

1 500 ml

2 200 ml

3 000 ml

3 700 ml

4 400 ml

5 200 ml

5 900 ml

1 524

1 800 ml

2 700 ml

3 700 ml

4 600 ml

5 500 ml

6 400 ml

7 300 ml

1 676

2 200 ml

3 300 ml

4 400 ml

5 500 ml

6 600 ml

7 700 ml

8 800 ml

Quantity required for a cased or artesian well

Cased wells are drilled when the groundwater is deep or the surface is rocky. They are generally made of steel pipe less than 80 millimeters in diameter and over 6 meters long.

Cased or Artesian Well

Height of the well water column (metres)

Well diameter





Millilitres of bleach


30 ml

60 ml

90 ml

120 ml


50 ml

100 ml

150 ml

190 ml


60 ml

140 ml

200 ml

270 ml


90 ml

190 ml

280 ml

400 ml


120 ml

250 ml

370 ml

500 ml


190 ml

380 ml

570 ml

800 ml


270 ml

540 ml

820 ml

1 100 ml

Calculation tool for disinfecting wells

New well Existing well

Well type: Tubular (Artesian)   Surface
Diameter:    Inches Centimetres Millimetres
Height of the well water column:     Feet   Metres  

You need to use litres or
  millilitres of 5% Javel water



The main sources of nitrates/nitrites are agricultural fertilizers, manure, household wastewater, and the decomposition of plant and animal organisms. Because they find their way into surface and groundwater through rain and melting snow, infiltration is greatest in the spring and fall.

Presence of nitrates/nitrites in my water

Over 5 mg/l 

A nitrate/nitrite concentration over 5 mg/l in a well generally indicates the influence of agricultural activities and calls for testing of this parameter at least twice a year, as concentrations can increase over time.

Over 10 mg/l 

If the concentration of nitrates/nitrites detected in the water exceeds the standard set out in the Regulation respecting the quality of drinking water, namely 10 mg/l, this water must not be used to prepare food for infants or pregnant women. Wherever possible, the general public must also avoid regularly consuming water whose nitrate/nitrite concentration exceeds the set standard. For more information on the applicable recommendations, those concerned are invited to contact their regional public health office (French).

Identifying the source of contamination

It is important to identify the source of contamination and carry out the necessary work. The contamination may be caused by the spreading of manure or chemical fertilizers near the well, or by nearby septic facilities. You can contact a representative of the regional office of Ministère du Développement durable, de l’Environnement et des Parcs in your area to help you find an appropriate solution.

My water still does not meet the quality standards

If all the aforementioned steps do not resolve the problem, it is still possible to obtain good quality water by installing one or more treatment devices specially designed to eliminate the problems revealed by the test results. Régie du bâtiment du Québec determines the requirements as to the type of treatment devices that can be installed in homes (French). To select the appropriate system, you can contact a firm specializing in water treatment. Products certified according to NSF/ANSI standards are recognized as effective in meeting the quality criteria. It is essential that such treatment systems be installed by a qualified professional, and used and maintained according the manufacturer’s recommendations.


Having my water tested…

To have your well water tested, it is recommended that you call on one of the laboratories accredited by the Ministère. The full list of accredited laboratories is updated regularly on the Ministère website. The laboratory will immediately notify the well owner if the water quality does not meet the established standards.

In addition to analysis of the aforementioned parameters, analysis of other parameters (hydrocarbons, solvents, pesticides, etc.) may be in order if pollution-generating activities are suspected in your area.

Adequate sampling methods are essential to ensure the validity of results. For more details, you can consult the division IV of Regulation respecting the quality of drinking water

It is generally recommended that you report any test results indicating that a chemical standard has been exceeded to the public health office in your area to obtain advice on water intended for human consumption. The contact information of the public health offices is available at the following Web address:

For more information

Contact the Ministère’s information center or the regional office in your area.

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