Ontario residents who rely on a private drinking water system can test it for bacterial contamination free of charge. Samples are not to be submitted from untreated surface water supplies such as lakes or rivers as these supplies are subject to contamination and are not considered suitable for drinking purposes unless properly treated. The Public Health serves as a drop-off point for water samples and there are many other drop of locations around the region. The samples are transported daily (Mon-Fri) to the Public Health Laboratory in London for testing. In order to have your sample tested, ensure that your sample is at a drop of location in time for the courier pick up. In addition, carefully read and fill out the requisition form. The lab will reject samples that are too old or have missing information. Temperature is also important; keep the sample refrigerated but do not freeze.


When taking a private water sample, please remember to:

  • Remove screen or other attachment from tap. 
  • Run cold water for 2 to 3 minutes before collecting sample in a Public Health Laboratory bottle. 
  • Do not touch the inside of the bottle or lid. 
  • Fill the sample bottle to the indicator line without rinsing the bottle. 
  • The granular material in the bottle is a Sodium Thiosulphate (a chemical that neutralizes chlorine) and is intended to be there. Do not rinse it out.  This material may cause a reaction if ingested or inhaled.
  • Attach the name label found on the bag to the bottle.  Place the completed form in the bag provided, and wrap the bag around the bottle (fold the top of the bag over to keep the bottle in the bag).


The Test Your Water video created by the Grey Bruce Health Unit demonstrates proper technique for taking a sample for testing water from a private source. Private water sources are any source not on a municipal water system and can include surface water, springs or groundwater (wells). View the Video




You may want to test your water for other parameters such as nitrates or other minerals and chemicals. Public Health does not offer these services. Wellaware.ca has information on how to obtain private testing for non-biological parameters.

Results are available by telephone from the London Public Health Lab provided you state the PIN number on the bottle (so be sure to record it before sending your sample).  Wait 72 hours after dropping off the sample, then call 1-877-723-3426 for your results.  Have your PIN number ready and an automated attendant will assist you. In addition results will be mailed to the return address on the reply form by the London lab.  Allow at least five days for return of results.


This Public Health Ontario website has lots of information on private water sampling.


Total Coliforms
(cfu/100 ml water)

E. coli
(cfu/100 ml water)


0 -5


The water is safe for drinking

6 or more

1 or more

The water is unsafe for drinking unless boiled or otherwise treated if 6 or more Total Coliforms are present or 1 or more E. coli or both.

Est (estimate)

Est (estimate)

The water is unsafe for drinking unless boiled or otherwise treated. (Coliform and E. coli counts are estimated, the plate is overgrown but the lab can determine the growth of some Coliform and E. coli colonies.)

o/g (overgrown)

o/g (overgrown)

The water is unsafe for drinking unless boiled or otherwise treated. (Coliform and E. coli counts cannot be determined because the test was overgrown with bacteria.)


The presence of Coliforms may be indicative of a contaminated water supply. Coliforms occur naturally in soil and decaying vegetation, but may also be associated with human or animal fecal contamination.

Low levels of Coliform bacteria (1 to 5) may be tolerated in a private water supply, provided at least 3 repeat samples have been taken over a six week period, the system is secure and not subject to contamination from other sources.

The persistent detection of more than 5 Coliform bacteria from any drinking water system indicates an unsafe condition.

E. coli

If any E. coli bacteria are present, water is considered unsafe for drinking. E. coli usually indicates fecal contamination from a human or animal source.

If you have tested your drinking water and found a problem and are unsure how to deal with it contact a Public Health Inspector at Public Health. They will be able to assist with the interpretation of the results and give advice on corrective actions. You can call us at 519-376-9420 or 1-800-263-3456, e-mail or drop in to our Owen Sound location.

The quickest way to temporarily produce safe water from water with bacteria in it is to boil the water (vigorous or rolling boil) for 1 minute. Some sources suggest longer times, but the Grey Bruce region is at a low enough altitude that 1 minute will be adequate. Don’t forget to use boiled water for washing fruits and vegetables, cleaning teeth, making ice, etc. You may also choose to use an alternative supply of safe water.

Your Public Health Inspector may suggest that you disinfect your well. Well disinfection is not a treatment system and should not be seen as a method of solving an ongoing issue. Well disinfection is an effective way of destroying pathogens that are present within the well and plumbing system at the time it is carried out. Well disinfection can resolve some temporary problems and should always be done following construction of a new well or work within a well. The information here is intended as a guide. If you are unsure about the process, contact a well driller who will be able to give you more advice and/or carry out the process for you.


Before you begin, disconnect or bypass any filters or treatment equipment that may be damaged by chlorine. You may need to check with the manufacturer, but typically equipment designed to reduce chemicals and odors are more likely to be affected than disinfection equipment such as UV systems. Consult the calculation tool below to determine the proper amount of unscented household bleach (5%) to disinfect the volume of water in your well.  Ensure you read and follow the manufacturer’s instructions when adding the disinfectant. Mix the household bleach with several litres of water before applying it to the well. Do not enter wells as they can be extremely hazardous. Turn on all faucets to distribute chlorinated water in the system until you can smell chlorine. Turn faucets off and allow the treatment to proceed for at least 12 hours. Drain the entire water system until the chlorine odor is no longer present. Do not drain this water into your septic tank system. Wait at least one day (2 or 3 days would be better) before collecting a sample for bacteriological testing. This is to ensure that you do not get a “false negative” which may make you believe your water is safe when it is not. Boil all drinking water, or use an alternative source until you receive a satisfactory laboratory report.


Public Health Ontario has developed this tool to help you work out how much chlorine you need to adequately disinfect you well.


Well disinfection tool



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