Definition
A boil water advisory — sometimes called a boil water notice or boil water order — is an official public health announcement telling residents to boil their tap water before drinking it, making ice, brushing teeth or preparing food. It means the water system may be, or is known to be, contaminated with harmful microorganisms such as E. coli, Giardia or Cryptosporidium that boiling can kill.
Advisories are preventive when a problem is possible (for example, a water main break dropped the pressure in the pipes) and corrective when testing has already found contamination. During an advisory, boiling water at a rolling boil for at least one minute makes it safe for drinking and cooking.
What triggers an advisory?
- A water main break, pump failure or power outage that depressurizes the distribution system
- Positive test results for total coliform or E. coli in the water supply
- Flooding, hurricanes and wildfires that overwhelm or damage treatment plants
- Loss of disinfection, filtration problems or turbidity (cloudiness) events at the treatment plant
- Cross-connections or backflow incidents that let contaminants enter the pipes
Who issues advisories in the United States?
In the U.S., the water system itself usually issues the notice — a city utility, a municipal authority, a private company or a rural water district — under rules enforced by the state drinking water program (for example TCEQ in Texas or a state Department of Health). The EPA sets national standards under the Safe Drinking Water Act, and states with primacy make sure systems comply, including the requirement to notify customers within 24 hours in most emergency situations.
Who issues advisories in Canada?
In Canada, drinking water is regulated provincially and territorially. Boil water advisories in provinces like Ontario, Québec, Manitoba, Saskatchewan, Nova Scotia and British Columbia are issued by provincial regulators, medical health officers or the water utility. For First Nations communities, Indigenous Services Canada and regional health authorities such as the First Nations Health Authority in B.C. track drinking water advisories publicly.
How long does an advisory last?
Most advisories last one to three days — roughly the time it takes to repair the problem and complete the required flushing and two consecutive rounds of clean bacteriological samples. Large incidents (hurricanes, floods, major plant failures) can keep advisories in place for a week or longer. An advisory is only over when the utility or health authority officially lifts it, so check this site, your utility’s alerts and local officials for the all-clear.
FAQ
Is a boil water advisory mandatory?
Yes. Although the wording differs by jurisdiction, an advisory (and especially a boil water order) is a legally binding public health directive. Ignoring it can put your household at real risk of waterborne illness.
Do I need to boil water for my pets?
Yes. Pets can get sick from the same organisms as people, so give them boiled or bottled water too.
Does boiling remove chemical contamination?
No. Boiling kills bacteria, viruses and parasites but does not remove most chemicals, fuel or heavy metals. For chemical emergencies, authorities issue do-not-drink or do-not-use notices instead, and bottled water becomes the safe option.