Boil Water Advisory: Exactly What to Do, What Not to Do, and When It's Safe Again

Water utilities issue boil water advisories when there is reason to believe that microbial contamination of the drinking water supply may have occurred or is suspected. The key word is "suspected" — advisories are often precautionary, meaning the utility isn't certain that contamination has occurred but the circumstances create a risk that warrants protective action.

The most common triggers include: water main breaks (which create a drop in water pressure that can allow soil and groundwater — potentially containing bacteria — to enter the distribution system through cracks or joints), loss of pressure in the distribution system (same mechanism, different cause), equipment failure at a treatment plant, flooding that may have compromised well water or surface water sources, and detection of bacteria or other pathogens in routine monitoring samples.

Boil water advisories can be issued for an entire water system or for a specific portion of it — for example, just the section of the distribution system affected by a pipe break.

The pathogens of concern during a boil water advisory are primarily bacteria (E. coli, Salmonella, Campylobacter), viruses (norovirus, hepatitis A, enteric adenoviruses), and protozoa (Giardia, Cryptosporidium). All of these are effectively killed by boiling at the temperatures water reaches at sea level.

Different types of advisories carry different urgency levels. A "boil water advisory" or "boil water notice" is the standard precautionary guidance. A "do not drink" order is stronger — it may indicate known contamination with chemical or other hazards that boiling cannot address. A "do not use" order is the most restrictive, covering all uses including bathing, and is typically issued only for severe contamination events.

Make sure you understand which type of advisory applies to your situation — the responses are different.

Boiling kills pathogens through heat denaturation of proteins and disruption of cell membranes and viral capsids. The key parameter is temperature — water heated to 212°F (100°C) at sea level kills all waterborne bacterial, viral, and protozoan pathogens within seconds.

The CDC recommendation is to bring water to a rolling boil for one full minute. At elevations above 6,500 feet, water boils at a lower temperature, so the recommendation extends to three minutes to ensure adequate pathogen kill despite the lower boiling temperature.

"Rolling boil" means vigorous, full bubbling — not just small bubbles forming at the bottom of the pot. Wait until you see an active, rolling boil across the surface, then maintain it for the required time.

After boiling, let the water cool before using it. Pouring hot boiled water into a clean, covered container and letting it cool is better than cooling it in an ice bath made with unboiled water — an easy contamination mistake. Store cooled boiled water in a sealed container (a clean pitcher with a lid, or capped bottles) in the refrigerator and use within 24 hours for drinking, or 48 hours for cooking purposes.

Label containers of boiled water if you have multiple containers of water in the house and might confuse boiled and unboiled. A simple piece of tape with "BOILED" and the date is enough.

Boiling does not remove chemical contamination — if your advisory is related to a chemical spill or detected chemical contaminant, boiling is not a solution and may concentrate chemicals by evaporation. In those situations, bottled water is the appropriate alternative.

This is where people often get confused. During a standard boil water advisory, the following activities require boiled or bottled water:

Drinking. Obviously — don't drink unboiled tap water directly. This includes water from refrigerator dispensers if they use tap water (even filtered tap water — the filter doesn't kill pathogens during a microbiological advisory).

Making coffee, tea, or any hot beverage. Even though these are made with hot water, the water may not reach a rolling boil and may not be held at temperature long enough to kill all pathogens. Use boiled water to make coffee and tea.

Making ice. Discard any ice made from tap water before or during the advisory. Don't use tap water in ice cube trays. For ice during an advisory, use boiled water that has been cooled, or use bagged ice from a store.

Brushing teeth. Use boiled or bottled water to brush teeth. This is one of the most commonly skipped precautions and one of the more significant ones — a small amount of water is ingested during tooth brushing and is a real exposure pathway.

Washing fruits and vegetables that will be eaten raw. Wash fresh produce with boiled water. Produce cooked in boiling water for adequate time is generally safe to eat without pre-washing with boiled water, as the cooking itself will kill pathogens.

Baby formula and food preparation. Use boiled or bottled water for all infant formula preparation. This is critical.

Washing wounds, cuts, or open sores. If you have any open wounds, use boiled or bottled water to clean them.

Cooking. Foods that are heated to adequate internal temperatures during cooking are generally safe — the cooking kills pathogens. But rinse produce in boiled water and use boiled water in cooking where the food might not reach pathogen-kill temperatures.

Showering and bathing for adults and older children. For healthy adults, showering and bathing in unboiled water during a standard microbiological advisory is generally considered safe. The key is to avoid swallowing the water. Be especially careful to keep water out of the mouths of young children during bathing — this requires active supervision.

For infants, the guidance is more cautious: sponge bathing with boiled water is recommended by some health departments during advisories, since infants are more likely to ingest water during bathing and are more vulnerable to waterborne illness.

Laundry. Washing clothes in an automatic washer is generally fine during a boil water advisory. The water in washing machines typically gets hot enough to be safe, and clothing is not ingested. Use normal laundry cycles.

Dishwashers. Commercial dishwashers that heat water to 170°F or above and include a sanitizing cycle are generally considered safe to use during a boil water advisory. Home dishwashers vary — if yours reaches a sanitizing temperature (check your owner's manual), it's likely safe. If you're unsure, hand wash dishes in boiled water and allow them to air dry completely (the drying phase is important, since wet surfaces support bacterial survival).

Toilet flushing. Safe. The water in toilet tanks and bowls is not a consumption exposure pathway in normal circumstances.

Watering plants. Generally safe for adult plants. For seedlings, sprouts, or any plant where water will contact produce that will be eaten fresh, use boiled water as a precaution.

Pets. Pets can get sick from the same pathogens that affect humans. Give your dogs, cats, and other pets boiled or bottled water during an advisory. Fish tanks using affected tap water are trickier — consult with a veterinarian if you're concerned.

Having tracked these events professionally for years, I can tell you the most common errors I see.

Forgetting about ice. This is probably the most common mistake. People boil their drinking water carefully, then put ice from their refrigerator dispenser — which uses tap water — into their glass of boiled water. The tap water in the ice cubes re-contaminates the boiled water. Discard all existing ice at the start of an advisory and don't make new ice from unboiled tap water.

Assuming refrigerator filters make water safe. Refrigerator water and ice filters are designed to remove taste, odor, and some contaminants. They are not designed to remove bacteria, viruses, or protozoa. A filter does not make tap water safe during a microbiological advisory.

Forgetting to boil water for tooth brushing. It feels excessive, but a meaningful amount of water is ingested during tooth brushing. Use boiled or bottled water.

Not telling guests or visitors. If someone visits your home during an advisory, they may not know to avoid tap water. A note on the faucet or a verbal heads-up is important.

Using hot tap water as a shortcut. Hot tap water from your water heater is not safe during a boil water advisory. The temperature in most home water heaters (typically 120°F) is below the temperature needed to kill all pathogens. Only water that has reached a rolling boil and been held there for one minute is safe.

Continuing to use a compromised well. If a boil water advisory applies to a private well — typically after flooding or a wellhead disturbance — don't assume that your water treatment system (softener, carbon filter, UV light) makes the water safe. Some of these systems may be compromised during the event that triggered the advisory, and none are rated to handle severely contaminated water. Use bottled water until testing confirms the well has been properly disinfected and retested.

The duration of a boil water advisory depends on what caused it and how quickly the underlying issue is resolved and verified. A routine advisory following a brief pressure loss during pipe repair may be lifted within 24–48 hours. An advisory following major flooding may last a week or more while the system is flushed, tested, and retested.

The process for lifting a boil water advisory follows a standard protocol. First, the utility fixes the underlying problem — repairing the pipe, restoring pressure, repairing the treatment plant equipment. Second, the utility flushes the affected section of the distribution system to remove potentially contaminated water and restore disinfectant residual. Third, the utility collects water samples from multiple points in the affected area and submits them to a certified laboratory for microbiological analysis. Fourth, if the results come back clean — typically requiring two consecutive rounds of satisfactory samples — the utility officially lifts the advisory and notifies customers.

This process takes time, and the timing is driven by laboratory turnaround rather than by public patience. Bacterial culture tests for coliform bacteria take 24 hours to produce results. If the first round of samples passes, a second round is collected and tested, adding another 24 hours minimum. The minimum practical timeline from "problem fixed" to "advisory lifted" is typically 48–72 hours even under ideal circumstances.

Do not assume the advisory has been lifted because a certain amount of time has passed, because you've heard neighbors say it's over, or because you received an automated phone call that seemed to say the issue was resolved but was actually about something else. Wait for official communication from your water utility explicitly stating that the boil water advisory has been lifted.

After the advisory is lifted: Flush your interior plumbing before resuming normal water use. Run cold water at each faucet for 2–5 minutes to flush any potentially contaminated water that may have entered your home's pipes during the advisory period. Run your refrigerator water dispenser for several minutes and discard the ice. Replace your refrigerator water filter if your system uses one and the filter is due for replacement. This post-advisory flushing is often forgotten but is an important final step.