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Environmental and Workplace Health

Boil Water Advisories and Boil Water Orders

What are boil water advisories and boil water orders?
Boil water advisories and boil water orders are public announcements advising the public that they should boil their tap water for drinking and for other uses noted below. They are preventative measures issued to protect public health from waterborne infectious agents that could be or are known to be present in drinking water. Boil water advisories are issued by either the local public health unit or other responsible authority, or by the water utility. Boil water orders are usually issued by the public health unit or other responsible authority.

What are the reasons for issuing boil water advisories or boil water orders?
A boil water advisory may be issued as a result of any of:

1) on evidence of conditions such as:

  • unacceptable levels of disease-causing bacteria, viruses or parasites in the water system anywhere from the source to the tap,
  • unacceptable levels in the cloudiness (turbidity) in the water at its originating source

These conditions can occur for many reasons including:

  • inadequate filtration and /or disinfection during treatment,
  • re-contamination during distribution,

2) precautionary measure when there is concern that contamination may occur, for example local emergency repairs in the distribution system

A boil water order is usually issued where evidence indicates that the drinking water is or may be responsible for an outbreak of illness.

Is it necessary to boil all water in the home during an advisory or order?
During boil water advisories or boil water orders, you should boil all water used for drinking, preparing food , beverages, ice cubes, washing fruits and vegetables, or brushing teeth. Severely immunocompromised individuals should always boil their tap water for the purposes noted above. Infant formulas should be prepared using boiled tapwater, at all times. In the event that boiling is not practical, your local public health authority or other responsible authority may direct you to disinfect the water using household bleach, or to use an alternative supply known to be safe.

It is not necessary to boil tap water used for other household purposes, such as showering, laundry, bathing, or washing dishes. Adults, teens, and older children can wash, bathe, or shower; however, they should avoid swallowing the water. Toddlers and infants should be sponge bathed.

How should tap water be boiled properly?
Water should be placed in a heat-resistant container or in an electric kettle without an automatic shut-off and brought to a rolling boil for 1 minute to kill all disease-causing organisms. Water can also be boiled in a microwave oven using a microwave-safe container, but it is advisable to include a glass rod or wooden or plastic stir stick in the container to prevent the formation of superheated water (water heated above its boiling point, without the formation of steam). The water should then be cooled and poured into a clean container or refrigerated until you are ready to use it. At elevations over 2,000 metres water boils at a slightly lower temperature and should therefore be boiled for at least two minutes to kill all disease-causing organisms.

I have a water treatment device, do I still need to boil my drinking water?
If the device is designed to improve the taste and odour or chemical quality of the water, such as activated carbon filters, it is still necessary to boil the water. Devices designed to disinfect the water, such as a UV light units, may be used as an alternative to boiling. If the water is cloudy, filtration may be required before disinfection. Check with the manufacturer if you are not certain.

Are extra precautions necessary during a waterborne outbreak?
In the event of a waterborne disease outbreak, public health or other responsible authorities may advise the public to wash their hands in a dilute solution of unscented household bleach and water (1 millilitre or 20 drops of unscented bleach per litre of water). This is particularly important before preparing or eating meals and after using the toilet, changing diapers, or handling animals. If dishes are washed by hand, they should be washed and rinsed in hot tap water, then soaked in a dilute solution of household bleach (20 millilitres of bleach in 10 litres of water) for 1 minute, and air dried. Dishwashers with a hot water cycle will disinfect dishes. These precautions should reduce the possible spread of illness and minimize the need to boil tap water.

When is a boil water advisory or order lifted?
Boil water advisories or boil water orders are usually lifted by the responsible authority or water utility when the water is considered safe and no longer poses a threat to public health.

What should I do when the boil water advisory or order has been lifted?
The responsible authority or water utility will provide instructions on flushing water pipes within the home. It is important to carefully follow the instructions provided. Water heaters may need to be disinfected and flushed to remove any contaminated water. Some types of water treatment devices may need to be disinfected or replaced before being used. Check with the manufacturer for details.

Is additional information on boil water advisories available?
For additional information on boil water advisories, consult the Health Canada document, "Guidance for Issuing and Rescinding Boil Water Advisories," available on the Health Canada website or contact your local public health unit. Information on disinfecting private wells is also available, or through your local public health unit.

For more information on drinking and recreational water quality issues?

or write to:

Water Quality and Health Bureau
Healthy Environments and Consumer Safety Branch
Health Canada,
Sir Charles Tupper Building,
2720 Riverside Drive (A.L. 6604B),
Ottawa, Ontario K1A 0K9