Health information, not medical advice. Test your own water and speak to your local health authority about what it contains. We may earn a commission when you buy through our links; it never affects our scores.
The short answer
During a boil water advisory, boil your tap water even if it’s filtered. CDC-based guidance says most household filters do not remove bacteria or viruses, and filtering, unlike boiling, will not eliminate all disease-causing microorganisms. Bring clear water to a rolling boil for 1 minute, or 3 minutes above 6,500 feet (CDC), or use bottled water. When the advisory lifts, follow your utility’s flushing steps; some health departments say to replace filters that ran during the advisory.
What is a boil water advisory?
It’s a notice from your water utility or health department that tap water may contain disease-causing germs, so it needs boiling before you drink it or cook with it. Boiling kills germs, but the CDC notes it does not remove chemicals. Follow the notice for your area; it may say how long to boil, and at higher elevations the EPA uses a lower threshold of 5,000 feet (EPA).
Does a water filter work during a boil water advisory?
Not reliably. Pitcher, fridge, faucet, and most under-sink filters use carbon, which is certified for chemicals such as chlorine and lead (NSF/ANSI 42 and 53), not bacteria or viruses (NSF). The CDC lists what it takes to remove each type of germ (CDC):
| Germ | What removes it (CDC) |
|---|---|
| Parasites (Cryptosporidium, Giardia) | Filters certified to NSF/ANSI 53 or 58 for cyst reduction, absolute pore size of 1 micron or smaller, or reverse osmosis |
| Bacteria | Absolute pore size of 0.3 micron or smaller, ultrafiltration, nanofiltration, or reverse osmosis |
| Viruses | Nanofiltration or reverse osmosis only |
Even with RO, CDC-based advisory guidance still says to boil. Certified home RO systems are typically certified for chemicals and dissolved solids under NSF/ANSI 58, not for bacteria and viruses.
Which certifications cover germs?
- NSF/ANSI 55 Class A UV systems inactivate bacteria, viruses, and cysts in contaminated water; Class B is only for nuisance bacteria in disinfected water (NSF). Class A needs visually clear water (Ohio Department of Health). The VIQUA PRO10 is a whole-house UV system certified by NSF International to NSF/ANSI 55 Class A.
- Protocol P231 covers microbiological purifiers (NSF). Few home systems are certified to it.
- NSF/ANSI 244 covers filters for public water that’s normally safe, against occasional contamination (NSF). It still isn’t a reason to skip an advisory.
What should you do during a boil water advisory?
- Drinking and cooking: use boiled or bottled water (CDC).
- Ice: don’t use ice from trays, dispensers, or ice makers; throw out ice made with tap water (CDC toolbox).
- Fridge water dispenser: don’t drink from it; its filter isn’t made to remove germs.
- Brushing teeth: use boiled or bottled water (CDC toolbox).
- Baby formula: prepare it with bottled water, or boiled water if bottled isn’t available (CDC toolbox).
- Dishes: a dishwasher is generally fine if its final rinse reaches 150°F or it has a sanitizing cycle (CDC toolbox).
- Showering: be careful not to swallow water (CDC toolbox).
- Can’t boil? The EPA gives bleach doses by strength: 8 drops of 6% unscented bleach per gallon of clear water, doubled for cloudy water; wait 30 minutes (EPA).
What should you do when the advisory ends?
Follow your utility’s notice. Guidance on filters differs:
- CDC (businesses): change all point-of-entry and point-of-use filters, and flush water-using equipment (CDC).
- Oakland County, Michigan: run cold taps for 5 minutes, flush the water heater, replace water filters, and make and discard three batches of ice (Oakland County).
- Pinellas County, Florida: run cold taps for at least 5 minutes; there’s no need to replace fridge or under-sink filters (Pinellas County).
If your notice says nothing about filters, replacing a carbon cartridge that filtered advisory water is the cautious choice. See how often to change a water filter and our fridge filter finder.
Common questions
Can I drink filtered water during a boil water advisory?
No, unless your utility says so. CDC-based guidance says to boil tap water even if it’s filtered (CDC toolbox).
How long do you boil water during a boil water advisory?
A rolling boil for 1 minute, or 3 minutes above 6,500 feet (CDC), unless your local notice says otherwise.
Does a water filter remove bacteria?
Most carbon filters don’t. The CDC says bacteria need an absolute pore size of 0.3 micron or smaller, ultrafiltration, nanofiltration, or RO (CDC).
Can I use my fridge ice maker during a boil water advisory?
No. Don’t use ice from dispensers or ice makers, and throw out ice made during the advisory.
Do I need to replace my water filter after a boil water advisory?
It depends on your health department. The CDC tells businesses to change all filters and Oakland County tells households to; Pinellas County says it isn’t necessary.
Sources
- CDC: Boil water advisory
- Maryland Department of Health (from the CDC Drinking Water Advisory Toolbox): What to do during a boil water advisory
- CDC: Preventing Cryptosporidium in commercial settings during a boil water advisory
- CDC: About choosing home water filters
- EPA: Emergency disinfection of drinking water
- NSF International: Standards for water treatment systems
- Ohio Department of Health: Ultraviolet light for continuous disinfection
- Oakland County, Michigan: After a boil water advisory
- Pinellas County, Florida: What to do after a boil water notice is lifted