Steps to take when E. coli is detected (1.0)

If E. coli has been detected in the original sample

Step 1

Immediately take all reasonable steps to notify all users of water from the system to use an alternate source of drinking water or to bring water to a rapid rolling boil for at least one minute before use. Post warning notices in prominent locations to alert users to use another source of drinking water. For designated facilities, for example schools or daycares, warning notices must be posted at every entrance to every building and every structure that is part of the designated facility.

Step 2

Immediately, at the same time that you are taking the actions in Step 1, report by phone or in person the adverse test result to the local medical officer of health (public health unit) and the Spills Action Centre (SAC) of the Ministry of the Environment and Climate Change (telephone 1-800-268-6060) and to any other parties as required.

Within 24 hours of giving verbal notice, provide the written notice to the local medical officer of health and SAC (by fax or in person) using the ministry’s Notice of Adverse Test Results and Other Problems and Notice of Issue Resolution at Drinking-Water System form. The form is available on the Ontario Central Forms Repository or by calling the Public Information Centre at 1-800-565-4923.

Step 3

Immediately, at the same time that you are taking the actions in Steps 1 and 2, resample at the original location and send the sample to the lab to be tested for E. coli.

If your plumbing lines supply water to numerous taps throughout your building or distribution lines run to multiple buildings, you will have an 'upstream" and/or "downstream" location from the original sampling location which gave rise to the adverse test result. You will also need to take samples from the closest upstream and downstream taps when you resample.

Step 4

Take any other actions as directed by the local medical officer of health.

Where the resample also detects E. coli

Step 5

Report any adverse resample test results as described in Step 2, and proceed with Step 6 below.

Step 6

Inspect the well-head and surrounding property and your plumbing to ensure that the system has been properly cons tructed and maintained to prevent entry of contaminants (see Appendix A – Well System Checklist in the Procedure for Corrective Action for Systems Not Currently Using Chlorine available by calling the Public Information Centre at 1-800-565-4923. Correct any problems identified before continuing with corrective action steps. Ensure signs are posted at the system to notify users to use an alternate source of drinking water.

Step 7

Shock chlorinate the well by pouring bleach or chlorine down the well to ensure that microbiological contamination is e liminated from the system. Leave the bleach in the well for at least 12 hours, without using the well. Next flush the water lines until you no longer can smell the chlorine in the tap water and then take resamples and test. (see Appendix C in the Procedure for Corrective Action for Systems Not Currently Using Chlorine for more details).

Step 8

Continue these corrective actions until E. coli is not detected in two consecutive sets of samples taken 24 to 48 hours apart or as otherwise directed by the medical officer of health.

Step 9

If these steps do not eliminate the contamination, contact a trained professional and follow the directions of the local medical officer of health.

Step 10

Within seven days of resolving the issues that gave rise to the contamination, submit a Notice of Issue Resolution, part of the Notice of Adverse Test Results and Other Problems form, to SAC and your local medical officer of health.

Steps to take when total coliforms are detected (2.0)

If total coliforms have been detected in the original sample

Step 1

Immediately report the adverse test result to the local medical officer of health (public health unit) and the Spills Action Centre (SAC) of the Ministry of the Environment and Climate Change (telephone 1-800-268-6060) and to any other parties as required. Within 24 hours of giving verbal notice, provide the written notice to the local medical officer of health and SAC (by fax or in person) using the ministry’s Notice of Adverse Test Results and Other Problems (O. Reg. 170/03) form.

Step 2

As soon as reasonably possible, resample at the original location (and possibly "upstream" and/or "downstream" as described in Step 3 in the E. coli section) and send the sample to the lab for testing.

Step 3

Take any other actions as directed by the local medical officer of health

Where the resample also detects total coliforms

Step 4

If a resample confirms the presence of total coliforms, report the result as described in Step 1, and follow Steps 6 to 10 outlined above in section 1 (Steps to take when E. coli is detected), replacing references to E. coli in Step 8 with total coliforms.

Post warning notices of potential problems (3.0)

You must post a warning notice to advise the staff, students and public if: you get adverse E. coli test results or you have not yet carried out required corrective actions.

Warning notices do not provide an exemption for testing or corrective action!

Post the notice in a prominent location where it is likely to be seen by those using water from the system. For designated facilities, warning notices must be posted at every entrance to every building and every structure that is part of the designated facility. Warning notices must be in a form provided by or approved by the ministry. You can obtain approved warning notices by calling the ministry’s Public Information Centre at 1-800-565-4923.

If you have not yet obtained warning notices, you can (as an interim measure) post any sign that states: "Public Notice: Do not drink this water" until you have received the ministry’s approved warning notice.

For more information

For more information visit the ministry’s drinking water web page or call the Public Information Centre at 1-800-565-4923.

Updated: July 15, 2021
Published: December 19, 2018