Boil water advisories are issued in Ontario when drinking water may be unsafe. These advisories help protect residents and businesses from harmful bacteria, viruses, and other contaminants.
A boil water advisory means tap water should be boiled before use until officials confirm the water is safe again.
Understanding what causes a boil water advisory—and knowing what to do during one—can help protect your health and prevent contamination.
In this guide, you’ll learn:
- What a boil water advisory is
- Why boil water advisories are issued
- Who issues advisories in Ontario
- What to do during an advisory
- How to safely use and store water
- What to do after an advisory ends
What Is a Boil Water Advisory?
A boil water advisory (BWA) is a public health warning issued when drinking water may contain harmful microorganisms or contaminants.
During a boil water advisory, tap water should not be consumed unless it has been properly boiled first.
Boil water advisories are usually temporary and remain in place until testing confirms the water is safe.
Why Are Boil Water Advisories Issued?
Boil water advisories are issued when water systems may be contaminated or at risk of contamination.
Common causes include:
Bacterial Contamination
Harmful microorganisms such as:
- E. coli
- Coliform bacteria
- Giardia
- Cryptosporidium
can enter drinking water systems and create health risks.
Water Main Breaks
Broken water mains or low water pressure can allow contaminants to enter pipes.
Sewage System Problems
Sewage backups or cross-connections can contaminate drinking water supplies.
Flooding and Severe Weather
Heavy rainfall, flooding, and storms can affect water treatment systems and water quality.
Chemical Spills or Industrial Pollution
Industrial accidents or chemical spills near water sources may trigger a precautionary advisory.
Who Issues Boil Water Advisories in Ontario?
Several organizations may issue boil water advisories in Ontario.
These include:
- Municipal governments
- Local public health units
- The Ontario Ministry of Health
- Indigenous Services Canada for First Nations communities
Residents can also check local public health websites for active advisories in their area.
What to Do During a Boil Water Advisory
If a boil water advisory is issued in your area, follow these important safety steps.
Boil Water Before Using It
Boiling water kills most harmful bacteria and microorganisms.
How to Properly Boil Water
- Bring water to a rolling boil
- Boil for at least 1 full minute
- Allow the water to cool naturally
- Store boiled water in clean containers
Use Boiled or Bottled Water for Drinking and Cooking
During a boil water advisory, only use boiled or bottled water for:
- Drinking
- Brushing teeth
- Cooking
- Preparing infant formula
- Washing fruits and vegetables
- Making coffee or ice
Be Careful When Washing Dishes
Hand Washing Dishes
Use boiled or bottled water when washing dishes by hand.
Using a Dishwasher
Dishwashers may be safe if they have a sanitizing cycle or reach high temperatures.
Bathing and Personal Hygiene
Adults and Older Children
Showering is generally safe, but avoid swallowing water.
Infants and Toddlers
Use boiled or bottled water for bathing young children.
Business Safety During a Boil Water Advisory
Businesses in food service, healthcare, and hospitality may need to adjust operations during an advisory.
Possible safety measures include:
- Using bottled water for food preparation
- Turning off soda fountains and ice machines
- Providing hand sanitizer
- Following Ontario safe drinking water regulations
How to Store Boiled Water Safely
Safe water storage is important during a boil water advisory.
Water Storage Tips
- Use clean glass or BPA-free plastic containers
- Keep containers sealed and covered
- Refrigerate boiled water when possible
- Use stored water within 24 to 48 hours
When Is It Safe to Use Tap Water Again?
A boil water advisory is lifted only after water testing confirms the supply is safe.
Always wait for an official notice before returning to normal water use.
What to Do After a Boil Water Advisory Ends
Once the advisory is lifted, follow these steps to clean your plumbing system.
Flush Household Pipes
Run cold water taps for at least 5 minutes.
Replace Water Filters
Replace:
- Fridge filters
- Faucet filters
- Water pitcher filters
Clean Ice Makers and Water Dispensers
Discard old ice and sanitize ice machines or dispensers.
Run Dishwashers
Run an empty sanitizing cycle before washing dishes normally.
How to Help Prevent Future Boil Water Advisories
Some water issues can be reduced through regular maintenance and monitoring.
Preventative Tips
- Test private well water regularly
- Maintain septic systems properly
- Install backflow prevention devices
- Monitor local water quality updates
Ontario recommends testing private well water at least 3 times per year.
Conclusion
Boil water advisories help protect public health when drinking water may be contaminated. Knowing how to respond can reduce health risks and keep your household or business safe.
If you receive a boil water advisory:
- Boil water before use
- Follow public health instructions
- Wait for official clearance before using tap water normally
Professional water testing and monitoring can also help identify potential water quality concerns before they become serious problems.
For expert water testing and compliance support, contact Canadian Water Compliance.
