Boil Water Advisories: What They Mean and What to Do

Advisories almost always trace to a loss of the system's physical or chemical safeguards rather than a confirmed outbreak. The common triggers: water main breaks and pressure drops (when pressure falls, contaminated groundwater can be sucked into cracked pipes); detected contamination, typically total coliform or E. coli in routine samples; treatment failures, like a chlorination pump fault or filter breach; and storms and floods that overwhelm plants or wash contaminants into source water. Most advisories are precautionary — issued because safety can't be verified, not because illness was found — which is also why most end without anyone getting sick.

Advisories typically last 24–72 hours: utilities must fix the underlying issue, flush affected mains, then collect bacterial samples on two consecutive days showing clean results before lifting the notice.

The procedure is the same one covered in our purification guide: bring water to a full rolling boil for 1 minute (3 minutes above 2,000 meters elevation), then let it cool covered and store it in clean, closed containers. This kills the bacteria, viruses, and protozoa an advisory is worried about. A kettle that reaches a rolling boil is fine; a coffee maker's hot plate is not, since brewing temperatures don't reliably hit boiling.

If you can't boil — power outage during the same storm that caused the advisory — unscented household bleach works as a fallback: 8 drops (about 1/8 teaspoon) per gallon of clear water, stirred and left 30 minutes. Sealed bottled water is the simplest answer for drinking if it's available; see our bottled vs tap guide for why it sidesteps distribution problems entirely.

• Drinking, including water for coffee makers, juice mixes, and refilling dispensers
• Ice — discard ice made during (and shortly before) the advisory; icemakers should be emptied and their first few post-advisory batches thrown out
• Brushing teeth and rinsing after — the same small-dose logic as brushing abroad, but here the water is confirmed suspect
• Food prep — washing produce, making infant formula (see our formula guide — formula deserves extra care during advisories), and any cooking where water isn't boiled for at least a minute anyway
• Pets — dogs and cats are susceptible to many of the same pathogens; give them boiled or bottled water too

Showering and bathing are fine for healthy adults and older children — just avoid swallowing water. Supervise young children in the bath (or sponge-bathe infants), since they drink bathwater with enthusiasm. Laundry is unaffected. Handwashing with soap and tap water is generally considered acceptable during precautionary advisories — scrub for 20 seconds and dry thoroughly, or follow with hand sanitizer if the advisory is for confirmed E. coli.

Dishwashing: a dishwasher with a sanitizing cycle or a final rinse above 66°C (150°F) is safe to use. For hand-washing dishes, wash with hot soapy water, then soak rinsed dishes for one minute in a sanitizing solution of 1 teaspoon of unscented bleach per gallon of water, and air dry. Or simply switch to disposables for a couple of days.

When the advisory ends, the water in your pipes, tank, and appliances is still the old water. Flush before trusting it:

• Run all cold taps for about 5 minutes (or per your utility's instructions), starting with the lowest tap in the building
• Run hot taps until the water heater has turned over — typically 15 minutes or more for a tank heater, since it holds a large volume of advisory-era water
• Icemakers: discard existing ice and the next 1–3 batches, and flush the supply line
• Refrigerator water dispensers and filters: flush per the manual; replace the filter cartridge, which may have trapped contaminants
• Water softeners and whole-house filters: run a regeneration cycle and replace filter elements as applicable

Apartment and office buildings with storage tanks may need longer flushing — building management should coordinate. Five minutes of running water is cheap insurance after several days of caution.