A boil water advisory is an official notice from your water utility or local government telling you that tap water may be contaminated and must be boiled before drinking. These advisories are issued when something has gone wrong with the water supply, whether a broken water main, a drop in water pressure, or the detection of harmful bacteria. The advisory stays in place until testing confirms the water is safe again.
Why Boil Water Advisories Happen
The single biggest cause is surprisingly mundane: water main breaks, distribution system repairs, and drops in water pressure account for about 80% of all boil water advisories in the United States, according to an EPA analysis. When a pipe breaks or pressure drops, untreated groundwater, soil, or sewage can seep into the system through the gap. Even after the pipe is fixed, bacteria may already be inside.
The remaining 20% stem from more serious triggers. These include detection of E. coli or other harmful bacteria in water samples, failures in treatment equipment, backflow events where water flows the wrong direction through a cross-connection, and natural disasters like floods, ice storms, or power outages that knock treatment plants offline. Flooding is especially dangerous because it can overwhelm water sources with sewage and runoff before treatment systems can compensate.
The contaminants that prompt an advisory can include bacteria and viruses (like norovirus or Shigella), chemical pollutants (like arsenic), toxins from harmful algal blooms, and in rare cases, radioactive materials. Most advisories, though, are about the risk of germs entering the system through a physical breach.
How to Boil Water Correctly
Bring clear water to a full rolling boil and keep it there for one minute. If you live at an elevation above 6,500 feet, boil for three minutes instead, because water boils at a lower temperature at high altitudes and needs more time to kill pathogens. Let the water cool naturally before using it, and store it in a clean, covered container. Bottled water is a safe alternative if you don’t want to boil.
If your water looks cloudy, filter it first through a clean cloth or coffee filter, then boil it. Cloudy water can shield bacteria from heat, making the boil less effective.
What You Can and Can’t Do With Tap Water
Use boiled or bottled water for anything that involves swallowing water or putting it near your mouth. That includes drinking, making coffee or tea, cooking, preparing baby formula, brushing your teeth, and washing fruits or vegetables. Ice made during the advisory should be thrown away.
Adults can shower or bathe in unboiled tap water as long as they avoid swallowing it. Be more cautious with babies and young children during bath time, since they’re more likely to swallow water accidentally. If you have open cuts or wounds, avoid exposing them to unboiled tap water.
Pets should also get boiled or bottled water during the advisory. The same bacteria that make people sick can affect animals.
Washing Dishes During an Advisory
Household dishwashers are generally safe to use if they reach a final rinse temperature of at least 150 degrees Fahrenheit or have a sanitizing cycle. If you’re washing dishes by hand, wash and rinse them with hot water as usual, then soak them in a separate basin with one teaspoon of unscented liquid bleach per gallon of warm water. Let them sit for at least one minute, then air dry completely before using them again.
How Long Advisories Typically Last
Most boil water advisories caused by a water main break last one to three days. The timeline depends on how quickly the utility can fix the problem and then prove the water is clean. In New York State, for example, an advisory can only be lifted after two consecutive rounds of water samples, taken at least 24 hours apart (or as close as 8 hours apart in some cases), show no coliform bacteria. For very small water systems with limited distribution, regulators may allow the advisory to end without sampling if the system has been fully flushed and all corrective work is done.
Advisories triggered by major disasters or widespread contamination can last much longer, sometimes weeks. Your water utility will notify you when the advisory is officially lifted. Don’t assume the water is safe just because the repair work looks finished.
What to Do After the Advisory Ends
Once the notice is officially lifted, run cold water at every faucet in your home for at least five minutes. This flushes out any water that was sitting in your household pipes during the advisory. You don’t need to use any special cleaning products on your faucets or fixtures. Just running the water through them is enough.
If you have a refrigerator with an ice maker or water dispenser, make one batch of ice and throw it away. The next batch will be safe. There’s no need to replace your refrigerator filter or any under-sink water filters; flushing the cold water lines clears out the system. Wash your pets’ water bowls with soap and water before refilling them. Your dishwasher, washing machine, and other water-using appliances don’t need any special cleaning or sanitizing once the advisory has ended.
Boiling Doesn’t Fix Everything
Boiling is effective against bacteria, viruses, and parasites, which is why it’s the go-to response for most advisories. But if the contamination involves chemicals, toxins, or heavy metals, boiling won’t help and can actually concentrate the contaminant by evaporating some of the water. In these situations, authorities may issue a “do not use” advisory instead, meaning you shouldn’t use the tap water at all, even after boiling. If your advisory specifies chemical contamination, bottled water is the only safe option until the notice is lifted.