Public Drinking Water


How can I be certain the water from a public water system is safe?

Public Health Inspectors and Ministry of Environment and Climate Change (MOECC) Inspectors monitor public drinking water systems to ensure a safe water supply. If water supplied by a system is unsafe either the system operator or public health will issue a boil water or drinking water advisory to protect the health of the system users. If your residence is connected to a private communal water system that does not meet the small drinking water system criteria you can contact the system operator to find out how the system is monitored to ensure safe drinking water.


Small Drinking Water Systems (SDWS)

If your business or premises makes drinking water available to the public and you do not get your drinking water from a municipal drinking water system, you may be an owner or operator of a small drinking water system. Systems serving designated facilities are not considered small drinking water systems and remain under MOECC regulation.

Small drinking water systems are regulated under Ontario SDWS Regulation 319. Public health inspectors (PHIs) conduct an on-site risk assessment for every small drinking water system. The system will be categorized as low, medium or high risk and the PHI will issue a directive outlining what the owner/operator of the system must do to keep the drinking water safe. The directive may include, but is not limited to, water testing requirements, treatment requirements, and operator raining.

SDWS are monitored by Public Health to ensure all requirements are being met and all adverse test results are reported to Public Health. Boil Water or Drinking Water advisories may be issued by the operator or Public Health to protect the health of the water system users in the case of an adverse bacteriological result, an adverse observation or an outbreak associated with the water system.


SDWS Resources, Documentation, and Requirements

Please see the Ministry of Health and Long-Term Care for more information on SDWS, related regulations, guidance documents, and fact sheets. If you are not sure whether your system is a SDWS or have further questions, please contact the Grey Bruce Health Unit.

The Government of Ontario Central Forms Site provides the following SDWS forms:


Other Resources

List of accredited drinking water laboratories (MOECC)

Chlorine Dilution Calculator - Public Health Ontario

Safe Drinking Water Act

Clean Water Act


SDWS Training and Education Resources

Grey Bruce Health Unit

The Grey Bruce Health Unit will be offering two workshops for owners and operators of Small Drinking Water Systems on March 4, 2019 and April 4, 2019. There is no cost to participate. Topics will include: roles and responsibilities of owner/operators, legal obligations, operational requirements, and more. Please see the pamphlet for additional information.

Registration deadline is February 28, 2019.

Small Drinking Water System Owner/Operator Workshop

SDWS Operator Guide 2018


If you would like to receive our SDWS newsletter and email notifications, please register for our contact list by sending an email to the Grey Bruce Health Unit. Please contact us if you do not have an email address.\


Walkerton Clean Water Centre

Please see the Walkerton Clean Water Centre (WCWC) for training courses for SDWS (O.Reg. 319) operators.  Fact sheets and other resources can be found on the WCWC website under the small systems zone (see My Resources for fact sheets) and on this webpage. For more information you can contact the WCWC by email or phone 519-881-2003 / 1-866-515-0550.


Boil Water Advisories or Orders, and Drinking Water Advisories

Boil Water Advisories, Boil Water Orders, and Drinking Water Advisories are public notices issued when conditions indicate that public drinking water is not safe for use. The type of notice issued will depend upon the problem with the drinking water and will indicate whether you can continue to use the water after appropriate treatment or if an alternative source of water is required.


Boil Water Advisory (BWA) or Order (BWO)

Boil Water Advisories are issued when conditions indicate that the water is not safe for consumption unless treated. E.g. biological contamination, loss of disinfection, loss of pressure in the system, or illness linked to the water system.

Boil Water Orders are issued by the Health Unit when required to protect the health of the water system users. The water can be used in the same manner as during a BWA.

Drinking Water Advisory (DWA)

Drinking Water Advisories are issued for adverse conditions when boiling or otherwise disinfecting the water will not render it safe for consumption, e.g. chemical contamination. Specific information regarding the water system will be provided to the water system users in these cases.

Precautionary Advisory

Precautionary advisories may be issued when there is a known possibility that the water may become contaminated, such as during repairs or maintenance to a water system. Precautionary notices are intended to protect the health of the users of the water system and are rescinded when the there is no longer a threat to public health.

Conditions for Rescinding a BWA, BWO, or DWA

BWAs, BWOs and DWAs are lifted by the water system operator or the Health Unit when the water is considered safe and no longer poses a threat to public health. This may be after biological or chemical testing indicates the water is safe.

Please see the fact sheets or contact the Grey Bruce Health Unit for more information.


Municipal Water Systems

Municipal water systems are operated by the city or town they service. The water system operators follow stringent procedures for monitoring the water quality as set out by Ministry of the Environment and Climate Change standards. The MOECC inspectors monitor the waterworks to ensure the water is treated, disinfected, sampled, and monitored as required. Any adverse test results are reported to Public Health and to the Ministry of the Environment and Climate Change Spills Action Centre. If water does not meet the standards of Ontario Regulation 169/03 Ontario Drinking Water Quality standards a Boil-Water or Drinking Water Advisory may be issued. You can obtain test results and other information from the municipality that operates the water system by contacting your local municipal office; some municipalities have reports available on their website. 


Fact Sheets


Walkerton Outbreak

Seven people died and thousands became ill from drinking contaminated municipal water that was not properly treated. Resulting regulations and reporting requirements are designed to prevent a situation like this from occurring again.


Walkerton E. Coli outbreak of May 2000


The community of Walkerton experienced an outbreak of illness that was linked to the municipal water supply. On Sunday May 21, 2000 the Medical Officer of Health issued a Boil Water Advisory to the residents of Walkerton. That Advisory was lifted on December 5, 2000.

An epidemiological investigation included both a descriptive study and a cross-sectional study. Intensive case-finding for the descriptive study ultimately led to the identification of 1346 reported cases of gastroenteritis with exposure to Walkerton municipal water. Among these, 799 were residents of the town of Walkerton. Based on estimates derived from the cross-sectional study, the number of Walkerton residents that became ill was approximately 1286. The overall estimated number of cases associated with the outbreak was over 2300 people.

Hemolytic Uremic Syndrome (HUS)

Under 10% of individuals with E. Coli 0157:H7 infection will develop Hemolytic Uremic Syndrome (HUS). HUS is a serious complication of E. Coli infection that may lead to kidney failure. Symptoms of HUS may include a decrease in the amount of urine produced, swelling in the face, hands, and feet, paleness of the skin, irritability and fatigue. Young children (especially under 5 years of age) and the elderly are most at risk for HUS. It is important to watch for the signs of HUS even after diarrhea has stopped.

Anyone with these symptoms, see your physician immediately.

The Investigative Report of the Walkerton Outbreak of Waterborne Gastroenteritis

Grey Bruce Health Unit Archived Documents



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