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Possible Health Effects of Drinking Contaminated Well Water

Fact Sheet Adobe Portable Document Format (PDF) 32KB

Many Halton Region residents living primarily in rural areas rely on privately-owned water sources such as wells for their drinking water.

Municipal water supplies in cities and towns are maintained and tested by Halton Region; however, privately-owned water sources are the responsibility of the homeowner or landowner. It is important that private well water be tested regularly – at least three times per year – and that the well be maintained at all times. Well owners may also wish to install additional drinking water disinfection devices to ensure that the water supplied from their wells is safe to drink at all times. 

Q: What is an unprotected water source?

    A: An unprotected water source refers to a stream, river, cistern, or poorly constructed well; or any well that is not properly drilled and does not have a watertight casing that extends to a depth of at least six meters below ground level. The safety of well water may also be influenced by the original water quality in the watershed or catchment.

    Unprotected water sources can easily become contaminated and unfit for drinking. 

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Q: What could happen if I drink contaminated water?

    A: The health effects of drinking contaminated water can range from no physical impact to severe illness or even death.

    Many factors affect the possible impact on health such as the age and general health status of the person, the type of contaminant, the amount consumed, and how long the person has been drinking the contaminated water.

    Some of the effects of drinking contaminated water can be immediate, while others may not be noticed for many years. These health effects can include gastrointestinal and stomach illnesses like nausea, vomiting, cramps, and diarrhea.

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Q: What could the water be contaminated with?

A: Private wells can become contaminated with bacteria or chemicals, such as nitrates.


Bacteria When a water test shows the presence of bacteria, it is considered unsafe to drink until the problem is fixed and the well is disinfected. The absence of bacteria in any one test does not ensure safety at other times. Regular testing throughout the year will establish your well water’s consistency and increase your confidence in its safety. Spring run-off, heavy rain events, or prolonged dry spells, as well as wear and tear of the well structures, or changes to the water catchment can all potentially affect the quality of your well water.


Total Coliforms Total coliform organisms are a group of bacteria that are commonly found in the environment, and are an indicator of the safety of your water. Total coliform bacteria, if present, indicate that disease-causing organisms (bacteria, viruses, parasites) could potentially be present in your water supply.


E. coli E. coli bacteria live only in the intestines of warm-blooded animals including humans. If any amount of E. coli bacteria is found in a water sample, it can be concluded that human sewage or animal faeces have contaminated the water supply.


NitratesThe presence of nitrates in well water is usually the result of farming activities like fertilizing, or seepage from septic systems. If nitrates are at levels above 10 milligrams per litre of water, an infant may suffer from a condition known as “blue baby syndrome” or methaemoglobinaemia. Blue baby syndrome is caused by the nitrates interfering with the blood’s ability to carry oxygen throughout the body.

Herbicides and PesticidesHerbicides and pesticides from both agricultural- and household-use can contaminate wells if used improperly or excessively. Always read and use the amount stated on the manufacturer's label.

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Q: Is there a taste, smell, or colour to contaminated water?

A: Many times the contamination is odourless, colourless, and tasteless.

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Q: What should I know about my water system?

1.     Know your watershed or catchment. Where does the water come from?

2.     Know your source (raw) water quality. How safe is the water that comes straight from your well before it enters any of your plumbing? Does it vary throughout the year?

3.     Know your treatment systems. Are your treatment systems improving the safety of your water adequately or are they making it worse because of the lack of maintenance, or because you are using the wrong systems or equipment?

4.     Know your distribution system. Are piping and plumbing intact everywhere? Are there cross-connections or is there backflow potential? Might plumbing materials add contaminants such as lead to the water?

These can be complex questions. You may need to discuss them with your local public health inspector. To speak with a public health inspector, call Halton Region at 905-825-6000, toll free 1-866-4HALTON (1-866-442-5866), or calling 311.

Only with all these components in place and regular assessment throughout the year can you have increased confidence in the quality of your drinking water. 

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Q: How can I test my well water?

1.     Obtain a water bottle and submission slip from Halton Region Health Department’s water depot locations. Place an order online at or by phone to receive a free sample bottle by mail.

2.     Remove the strainer screen from your household tap. Disinfect the end of the water tap with an alcohol swab or diluted bleach solution (1 part household bleach to 10 parts water).  Run cold water through the tap for 3 to 4 minutes to remove standing water from your plumbing system.

3.     Fill the bottle to the indicator line directly from a household tap without rinsing the bottle or bottle cap. Do not touch the bottle lip, inside of the lid, or inside of bottle – never set the lid down.

4.     Fill out the submission slip. Provide your full address, including your postal code, telephone number and other required details. Note: The Halton Region Health Unit number is 2236.

5.    Return the water sample and submission form to your nearest Health Department water depot location during the specified water depot hours. The water sample will be sent by courier to the Hamilton Public Health Laboratory. Halton Region is not responsible for lost results. Water samples must be dropped off within 24 hours of being collected. The sample should be refrigerated unless dropped off immediately.

Three ways to get well water test results:

There are three ways you can get the results of your well water test:

1.     Results will be mailed to you in 7-10 business days from the day the sample is submitted to the lab.

2.     Call 1-877-723-3426 for test results after 4-5 business days from the day the sample was submitted. Give your PIN number located on the side of the water sample bottle.

3.    Pick-up your results at the Public Health Lab, 250 Fennell Avenue, Hamilton. Call 905-385-5379 or 1-866-282-7376.


Other Tests – 

The Health Department will test water for nitrates free of charge. Please contact the Health Department to arrange for a nitrate test.

Although the Health Department does not offer testing for substances other than bacteria or nitrates, public health inspectors are available to advise you about other tests that may be done in relation to a specific health issue