Boil Water Advisory: What It Means, What Is Safe to Use, and How to Disinfect at Home

Key points

• A boil water advisory means the tap water may carry germs that heat will kill. Bring clear water to a full rolling boil for 1 minute (3 minutes above 6,500 feet), then let it cool.

• A do-not-drink or do-not-use order is a different animal. Boiling does not fix chemicals, and on a do-not-use order the water is not safe to touch either.

• The advisory covers more than the drinking glass. Ice makers, coffee makers, brushing teeth, rinsing produce, baby formula, pet bowls, and humidifiers all need safe water.

• Showering, handwashing with soap, hot dishwasher cycles, and laundry are generally still fine.

• If you cannot boil, unscented household bleach at the exact CDC and EPA ratio works on most germs, but it is weak against Cryptosporidium. Boiling or a filter rated for parasites is the fix there.

A boil water advisory almost never arrives because something dramatic happened at the treatment plant. It usually arrives because a water main broke down the street and the pressure in the pipes dropped. In 2021, the EPA counted 4,036 boil water advisory events across the country, and about 80 percent of them traced back to main breaks, distribution repairs, and loss of pressure. Only about 6 percent involved confirmed contamination.

That is good news and bad news. Good, because most advisories are precautionary. Bad, because "precautionary" makes people sloppy, and the mistakes are always the same three: the ice maker, the coffee pot, and the toothbrush.

Advisories also cluster during storm season, when main breaks and power failures arrive in batches, which is why safe water sits near the top of our 72-hour hurricane preparedness checklist. Here is what the advisory actually means, what you can keep using, and exactly how to make water safe when you cannot boil it.

What does a boil water advisory actually mean?

It means your water utility believes the water leaving your tap may contain disease-causing germs, and that boiling will kill them. The CDC is direct about why boiling is the default answer: boiling is the surest way to kill disease-causing organisms, including viruses, bacteria, and parasites.

Advisories go out for things like a main break, a pump failure, a power outage at a lift station, a pressure loss during a hydrant flush, inadequate disinfection at the plant, or a positive bacteria sample. When pressure drops in a distribution line, groundwater and whatever is in the soil around the pipe can be drawn in through joints and cracks. Nobody knows in that moment whether anything actually got in. So the utility tells everyone to boil until follow-up samples come back clean, which usually takes 18 to 48 hours because the lab needs time to incubate them.

That waiting period is why advisories feel so open-ended. It is not that officials are being cagey. It is that bacteria grow on their own schedule.

What is the difference between a boil water advisory, a boil water notice, and a do-not-use order?

An advisory and a notice mean the same thing. A do-not-drink or do-not-use order does not, and that difference is the one worth memorizing.

The New York State Department of Health addresses the first half head on. In its guidance for water suppliers, it notes that some people consider an advisory more precautionary than a boil water notice, but both a notice and an advisory can be written in precautionary terms and there is no real difference. A "boil water order" is the directive the health department issues to the utility. A "notice" or "advisory" is what the utility sends to you. Treat all three words as the same instruction: boil it.

The CDC's overview of drinking water advisories then separates out the two that are genuinely different:

• Boil water advisory. Germs are the concern. Heat solves it. Boil for drinking and cooking, or use bottled water. Handwashing with tap water and soap is generally fine.

• Do not drink. The water contains something boiling will not remove, such as a chemical, a toxin, or a fuel spill into the system. Boiling can make it worse by concentrating what is there. Use commercially bottled water for drinking, cooking, brushing teeth, and making ice.

• Do not use. Rare, and the most serious. Contact with skin, lungs, or eyes is considered dangerous, so showering and handwashing are off the table too. Bottled water for everything until officials lift it.

If you get a do-not-drink or do-not-use order and someone in the house has already swallowed the water, call Poison Control at 1-800-222-1222. They are free, staffed 24 hours, and they would much rather field a question that turns out to be nothing. If the person is unconscious, having trouble breathing, or having a seizure, call 911 first.

How long do you have to boil water during a boil water advisory?

One minute at a full rolling boil at normal elevation, and 3 minutes above 6,500 feet. The CDC's instruction is to bring clear water to a rolling boil for 1 minute, and at elevations above 6,500 feet, boil for 3 minutes.

Two details matter more than the number itself.

First, "rolling boil" is not a mood. It means big bubbles breaking the surface continuously, not the small bubbles clinging to the side of the pot at the start. Start the clock when the surface is genuinely rolling.

Second, if the water is cloudy or discolored, deal with that before you boil. The CDC says to filter it through a clean cloth, paper towel, or coffee filter, or let it settle and draw off the clear water on top. Sediment shields germs from heat and makes chemical disinfection much less reliable.

Why longer is not better

Boiling for 10 minutes does not make water 10 times safer. The pathogens that matter in drinking water are done well before the minute is up, which is why 1 minute is the number every agency lands on. What extra boiling does accomplish is evaporating your water and burning your fuel, which is a real cost during an outage when you may be running a camp stove on a finite propane canister.

There is a subtler problem too. The EPA is explicit that boiling or disinfection will not eliminate heavy metals, salts, and most other chemicals. Those stay behind while the water leaves as steam. Boiling a pot down by a third does not reduce the lead or the nitrate in it. It leaves the same amount in less water.

One honest note on the altitude number. The CDC uses 6,500 feet as the threshold for the 3-minute boil, while the EPA's emergency disinfection page uses 5,000 feet. If you live between those two marks, just boil for 3 minutes. The extra 2 minutes cost you nothing.

What does a boil water advisory cover that people forget?

Everything the water touches on its way into a person, which is a longer list than most people picture. The CDC fact sheet distributed to water systems tells households to use boiled or bottled water to wash all fruits and vegetables, cook food, prepare drinks such as coffee, tea, and lemonade, and wash food preparation surfaces, on top of the obvious drinking and tooth brushing.

The ones that get missed:

• The refrigerator ice maker. It has been quietly making contaminated ice on a plumbed line the whole time. Dump the bin, turn the maker off, and do not restart it until the advisory clears. Ice does not sterilize anything. Freezing preserves germs.

• The drip coffee maker. A home brewer heats water to roughly 195 to 205 degrees F, but only holds it there for seconds as it passes through the grounds. That is not a reliable 1-minute boil. Boil the water first, let it cool, then brew, or use bottled water.

• Brushing teeth. You swallow more of it than you think, and children swallow considerably more. Use boiled or bottled water, including for rinsing the brush.

• Rinsing produce. Lettuce, berries, and anything eaten raw. Rinsing in contaminated tap water is worse than not rinsing at all.

• Baby formula. The CDC's order of preference is breastfeeding first, then ready-to-feed formula, then powdered or concentrated formula mixed with bottled water, and boiled water only if bottled is unavailable. Bottles and nipples get sterilized with safe water too.

• Pet bowls. Dogs and cats catch some of the same waterborne bugs people do. The same guidance says to give them bottled water, or boiled water that has been cooled.

• Humidifiers, CPAP reservoirs, and nasal rinse devices. This one is not just an advisory problem. The CDC recommends distilled or boiled and cooled water in humidifiers even on an ordinary day, because germs can live in humidifiers and spread through the mist humidifiers make. For nasal rinsing the language is blunter: never use water straight from the tap to rinse your sinuses. Some organisms that are harmless to swallow are not harmless in your nose.

What is still safe to use during a boil water advisory?

More than you would guess, and this is the part that keeps a household from burning through 40 gallons of bottled water in 2 days. If you are not sure you have that much on hand, start with how much water to store per person and count what is actually on the shelf.

• Showering and bathing, for healthy adults. Keep your mouth closed and do not swallow the water. Sponge bathe infants and small children instead, since they cannot be trusted not to drink the bathwater. If you have an open wound or a fresh surgical site, ask your doctor first. The CDC warns that open wounds and rashes that have been exposed to contaminated water can become infected.

• Handwashing with soap and running tap water, for at least 20 seconds, unless your local health officials say otherwise. Soap and mechanical scrubbing do the work. Hand sanitizer with at least 60 percent alcohol is the backup.

• The dishwasher, if it runs hot enough. A machine with a sanitizing cycle or a final rinse of about 150 degrees F or higher is fine. For hand washing, wash and rinse as usual, then soak the dishes in a bleach sanitizing solution for at least a minute and air dry.

• Laundry. Normal loads, normal machine, no special steps.

• Flushing toilets. Always fine on a boil advisory. The only time this changes is a do-not-use order or a sewer system failure.

How do you disinfect water with bleach when you cannot boil?

You add a very small, measured amount of unscented household bleach and wait 30 minutes. The exact dose depends on the bleach concentration printed on the bottle, and that number is not the same across brands.

The CDC's current instruction for clear water is to add 8 drops, a little less than one eighth of a teaspoon, of 5 to 9 percent unscented household bleach to 1 gallon of water, then let it stand at least 30 minutes before drinking. For cloudy water, double it to 16 drops (a quarter teaspoon) per gallon, after filtering or settling it first.

The EPA breaks it out by concentration, which is more useful if you actually read your bottle:

• 6 percent sodium hypochlorite: 8 drops per gallon

• 8.25 percent sodium hypochlorite: 6 drops per gallon

• Stir, let stand 30 minutes, then smell it. The water should have a slight chlorine odor. If it does not, repeat the dose and wait another 15 minutes.

That smell test is the closest thing you have to a home assay. No chlorine smell after 30 minutes means the chlorine was consumed by organic material in the water, which means there was not enough left over to finish the job.

The bleach rules that are not optional

• Unscented only. The EPA says do not use scented, color safe, or bleaches with added cleaners. Those additives are not meant to be swallowed, and the label percentage on them does not tell you what you are actually drinking.

• Check the concentration on the label. Household bleach has been sold at 2.75 percent, 5.25 percent, 6 percent, and 8.25 percent depending on the era and the brand. Dosing an 8.25 percent bottle at the 6 percent rate overshoots. Dosing an old weak bottle at the strong rate leaves you under-treated.

• Bleach ages. Sodium hypochlorite loses potency on the shelf, faster when it is warm. A bottle that has sat in a hot garage for 2 years is not delivering its label strength. Rotate it about once a year if you keep it as a water treatment item.

• Never mix bleach with ammonia or acid cleaners. That produces toxic gas. If you have mixed them and are having trouble breathing, get to fresh air and call 911.

Why does bleach not handle Cryptosporidium?

Because Cryptosporidium wraps itself in a tough shell called an oocyst that chlorine simply cannot get through at the doses used in drinking water. The CDC states it plainly in its guidance for commercial kitchens: Cryptosporidium is poorly inactivated by chlorine or iodine disinfection. Its emergency water page carries the same warning, that disinfectants do not work as well as boiling for killing some germs, including the parasites Cryptosporidium and Giardia.

This matters because Cryptosporidium is the leading cause of waterborne disease in the United States, and it is exactly the kind of thing that gets into a distribution system when pressure drops near a sewer line.

You have two reliable answers:

1. Boil. Heat does not care about the oocyst shell. One minute at a rolling boil handles it.

2. Filter with something rated for it. The CDC's caution is that most portable water filters do not remove bacteria or viruses, and that you should choose a filter labeled to remove parasites and follow the manufacturer's instructions. Look for an absolute pore size of 1 micron or smaller, or a label that says it meets NSF/ANSI Standard 53 or 58 for cyst reduction. If you want to understand where filter media actually stops and starts, our breakdown of what an activated carbon filter removes and what it does not covers the gap in plain terms.

Chemical treatment is the fallback when boiling is impossible, not the equal of it. If you want the full ladder of no-power options, we walked through all of them in how to purify water in an emergency without electricity.

What do you do when the boil water advisory is lifted?

You flush the pipes before you trust them. The water in your house did not clean itself when the utility sent the all-clear text. That message only means the water in the street is clean. Everything sitting in your service line, your fixtures, your water heater, and your appliances is still the old water.

The CDC's recovery guidance for facilities lays out the sequence, and it scales down to a house without much change:

1. Run every cold water tap until you get water that is clearly coming from the street rather than from your pipes. The CDC's facility guidance calls for flushing for more than 5 minutes until you detect residual disinfectant. Five minutes per fixture is a good household rule. Start at the tap closest to where the water enters and work outward. Take the aerators off first if you can, they trap sediment.

2. Then run the hot taps for a few minutes each, so the water heater cycles fresh water through. If the advisory ran more than a few days, consider draining and refilling the heater.

3. Dump all the ice made during the advisory and for a few hours before it started. Then clean and sanitize the ice maker per the manufacturer's instructions, run and discard the first 2 or 3 batches, and only then start keeping ice again. The CDC's commercial guidance is to discard ice from ice machines, then clean and sanitize them.

4. Replace point-of-use and point-of-entry filters. This is the step almost nobody does, and it is the one the CDC calls out specifically: change all point-of-entry and point-of-use filters. That means the refrigerator filter, the pitcher filter, the under-sink cartridge, and the faucet-mount unit. A carbon filter that has been straining contaminated water for 2 days is now a place where bacteria can grow, and it will keep seeding your "filtered" water after the advisory ends. Flush the fixture for several minutes with the old filter out before you install the new one.

5. Run and drain water-using appliances. Run the dishwasher empty on a hot cycle. Regenerate a water softener if you have one. Flush the water dispenser line on the refrigerator.

6. If you have a private well that flooded or lost pressure, none of this applies to you the same way. The well itself needs shock chlorination and a bacteria test before it goes back into service.

Where each method runs out of road

Every method here has an edge, and knowing where it is keeps you from trusting the wrong tool at the wrong time.

• Boiling kills germs and does nothing else. The CDC is explicit that boiling does not remove chemicals. If the advisory is a do-not-drink chemical event, the pot on the stove is the wrong answer.

• Bleach handles most bacteria and viruses, is weak against Cryptosporidium and Giardia, and does nothing for chemicals, metals, or nitrate. It also degrades on the shelf.

• Carbon filters improve taste and pull some chemicals. Most do not remove bacteria or viruses unless they are specifically certified to.

• Anything is defeated by water contaminated with fuel, solvents, bulk sewage, or floodwater. The CDC's blanket statement is that water contaminated with harmful chemicals or toxins cannot be made safe by boiling, disinfecting, or filtering.

When to stop improvising and get help

Call your doctor or clinic if someone in the house has diarrhea lasting more than 2 days, bloody stool, a fever above 102 degrees F, or signs of dehydration (very little urine, dizziness on standing, dry mouth). Call sooner if the person who is sick is an infant, over 65, pregnant, or has a weakened immune system. Cryptosporidiosis in particular can be serious and prolonged for someone immunocompromised.

Call Poison Control at 1-800-222-1222 for any suspected chemical exposure from tap water, or if someone swallowed water during a do-not-drink order. Call 911 for trouble breathing, chest pain, confusion, or unconsciousness.

And call your utility, not a neighbor's Facebook post, to find out whether the advisory is still active. Utilities are required to notify you when it lifts.

Frequently asked questions

Can I drink filtered refrigerator water during a boil water advisory?

No. A standard refrigerator filter is a carbon filter built for taste and chlorine, not for pathogens, and it is not certified to remove bacteria or viruses. The water going into it is the same water in the advisory. Treat the fridge dispenser and the ice maker as unsafe until the advisory lifts, then replace the filter before you use them again.

How long do I boil water during a boil water advisory?

One minute at a full rolling boil, or 3 minutes if you are above 6,500 feet in elevation, per the CDC. Let it cool on its own rather than adding ice or cold tap water. Store the cooled water in clean, covered containers.

Is it safe to shower during a boil water advisory?

Generally yes for healthy adults and older children, as long as you do not swallow the water. Sponge bathe infants and toddlers instead. If you have an open wound, a recent surgical site, or a weakened immune system, check with your doctor. A do-not-use order is the exception, and there you do not use the tap at all.

Can I use bleach instead of boiling during a boil water advisory?

Only as a fallback. Use 8 drops of unscented 5 to 9 percent household bleach per gallon of clear water (16 drops if cloudy), stir, and wait 30 minutes. It should smell faintly of chlorine. Bleach is much weaker than boiling against Cryptosporidium and Giardia, and it does nothing for chemicals, so boiling is the better choice whenever you have heat.

What do I do with my ice maker after a boil water advisory ends?

Throw out all the ice, clean and sanitize the machine per the manufacturer's instructions, replace the water filter, then run and discard the first 2 or 3 batches before you start keeping ice again. Ice made during the advisory is not safe just because it froze.

Do I need to boil water for my dog during a boil water advisory?

Yes. CDC guidance is to give pets bottled water or boiled water that has been cooled, the same as people. Wash the bowls in the dishwasher on a hot cycle, or by hand with a bleach sanitizing soak.

You never know, but you can always be ready.

Sources: CDC, How to Make Water Safe in an Emergency | CDC, Drinking Water Advisories: An Overview | CDC, Boil Water Advisory | EPA, Emergency Disinfection of Drinking Water | CDC, Preventing Crypto in Commercial Settings During a Boil Water Advisory | CDC, Guidance for Water System Repair and Recovery Following a Boil Water Alert | CDC, Preventing Waterborne Germs at Home | CDC, Guidelines for Personal Hygiene During an Emergency | EPA, National Occurrence of Boil Water Advisories | New York State Department of Health, Boil Water Notices Fact Sheet | CDC fact sheet, What to Do During a Boil Water Advisory (via Louisiana Department of Health)