What a boil water advisory actually means

What triggers a boil water advisory

A boil water advisory is issued when a public water system has reason to believe the water may be contaminated with biological pathogens — bacteria, viruses, or protozoa. Common causes include water main breaks (which can introduce contaminants through pressure loss), flooding that overwhelms treatment capacity, equipment failures at treatment plants, and natural disasters that damage distribution infrastructure.

The advisory is a precautionary measure. In many cases, the water may still be safe — the utility issues the advisory while testing confirms the system is clear. In others, contamination is confirmed. Either way, the appropriate household response is the same: treat all tap water as potentially contaminated until the advisory is lifted.

Boil water advisories are distinct from Do Not Use orders. A Do Not Use order means the water should not be used for any purpose, including washing or bathing. A boil water advisory means the water can be made safe for most purposes through boiling or chemical treatment.

The boil water protocol — exactly

The CDC boil water guidance is specific. Bring water to a rolling boil for one full minute. At elevations above 6,500 feet, boil for three minutes to account for the lower boiling point. Let the water cool before using it. Store boiled water in a clean, covered container.

Boiled or bottled water should be used for:

• •Drinking and making ice
• •Cooking and food preparation, including washing produce
• •Brushing teeth
• •Making baby formula and infant food
• •Washing dishes by hand (use boiled water for the final rinse, or run dishwasher at highest heat setting)
• •Preparing pet food and pet water

Showering and bathing are generally safe during a boil water advisory, with caution: do not swallow water, and take care with young children and people with weakened immune systems who may be more susceptible if water contacts the mouth or eyes.

What most people miss

Refrigerator water dispensers and ice makers. The filtered water and ice in your refrigerator was made from tap water during the advisory period. Discard all ice made during the advisory. After the advisory is lifted, flush the water dispenser for two to four minutes and replace the refrigerator filter before using it again.

Whole-house and point-of-entry filters. Filters exposed to potentially contaminated water during an advisory period may harbor pathogens. Replace or disinfect filter cartridges after the advisory is lifted, following the manufacturer's guidance for your specific filter type.

Countertop gravity filters. Do not run untreated advisory water through a gravity filter during a boil water advisory unless the filter is specifically rated for pathogen removal (such as ProOne or British Berkefeld). Carbon-only gravity filters do not reliably remove bacteria and viruses. Use boiled water or commercially bottled water instead.

When the advisory is lifted

After a boil water advisory is officially lifted by your utility — not based on informal reports or social media — flush household plumbing before returning to normal use. Run all cold water faucets for two to three minutes, flush toilets two to three times, and run appliances that use water (dishwasher, washing machine) through one cycle. The CDC recommends running faucets beginning with the lowest floor and working upward to clear any residual contamination from interior plumbing.

What to do right now

1. 1 Know how to find advisories for your area. Your water utility's website and emergency alert system are the authoritative sources. Sign up for your local emergency notification system if you have not already.
2. 2 Keep purification tablets in your kit. When an advisory is issued without warning, tablets let you treat water without waiting for a boil. Potable Aqua or Aquamira work in minutes and store for years.
3. 3 Store enough water to cover a 72-hour advisory without any tap water at all. Most boil water advisories resolve within one to three days. A 72-hour supply at 1.5 gallons per person is your buffer to handle an advisory calmly.
4. 4 Print this protocol and keep it with your kit. When an advisory is issued, you will not want to search for the steps. One laminated card in the emergency supplies is more useful than a bookmarked page you may not be able to access during a power outage.