A water boil advisory is a public notice from your water utility or health department warning that your tap water may be unsafe, because it could contain harmful microbes such as bacteria, viruses, or parasites. Until it’s confirmed safe, you’re asked to boil it first (or use bottled water) for anything you’ll swallow.
Most are precautionary, issued the moment conditions could let germs in, like a main break or a drop in pressure, not because anyone was made sick. And boiling only fixes that one problem: it kills living germs but does nothing for chemicals like PFAS or lead, which is why there’s more than one kind of notice.
Three main advisories exist, and the right response depends on which one your utility issued.
a.k.a. boil water notice / boil order
chemical contamination
avoid all contact
First, read the notice to see which type it is. Then follow the matching steps. These reflect current CDC guidance.
Make water safe: bring clear tap water to a rolling boil for 1 minute (3 minutes above 6,500 ft), let it cool, and store it covered. Or use bottled water. No stove? Disinfect clear water with unscented household bleach: about ⅛ teaspoon (8 drops) per gallon, then wait 30 minutes.
Flush your pipes: run cold taps for about 5 minutes, flush the water heater, run and discard several batches of ice, and replace water filters.
Do not boil the water. Boiling will not remove chemicals such as PFAS or lead and can concentrate them.
A certified home filter or Spout can reduce chemical contaminants like PFAS and lead. See our guide to home water filters. If in doubt about which notice you have, contact your water provider, the number is on your bill and on the notice.
The five biggest pressures on America’s water systems, and what each one means for what comes out of your tap.
The single biggest driver. When a main breaks or system pressure drops, untreated groundwater and contaminants can be pulled into the pipes. In our first-party data, main or line breaks alone account for 46% of advisories with a stated cause, more than the next four causes combined.
Read more →A routine sample comes back positive for total coliform or E. coli, signs that disease-causing organisms could be in the supply. Boiling is effective here: it kills bacteria, viruses and parasites.
Read more →Much of the U.S. distribution network is decades old. The EPA estimates about 9 million lead service lines are still in use; its 2024 Lead and Copper Rule Improvements require utilities to replace them within 10 years. Old, failing pipes break more often (a boil advisory), and lead itself is a chemical that boiling cannot remove (a Do Not Drink concern).
Read more →“Forever chemicals” (PFAS) and other chemical pollutants do not respond to boiling; in fact, boiling concentrates them. In 2024 the EPA set the first national drinking-water limits for PFAS: 4 parts per trillion for PFOA and PFOS. These trigger a Do Not Drink notice, not a boil advisory.
Read more →Extreme weather overwhelms water systems. Flooding can swamp treatment plants and wells; wildfires can damage pipes and draw chemicals into the network; hard freezes burst mains and knock out pressure. Each can put a community under a boil advisory.
Read more →For a year (June 2025 to May 2026) we tracked public utility water notices from across the country, logging what caused each one and mapping where it happened.
Behind most advisories lies one core problem: America’s aging water infrastructure system.
These categories overlap. Severe weather (freezes, floods, storms) can itself cause many of the main breaks, pressure losses and contamination events counted above, so the true footprint of weather is larger than the 5.7% shown here.
Based on the 1,001 of 1,485 notices between June ’25 – May ’26 that named an actual cause.
Each point is a community that issued at least one advisory.
Read the map as coverage, not a hazard ranking. Data pulled from water boil advisory notices issued across the US between June ’25 – May ’26. It is not a complete list of every advisory issued over that time period.
Note: these figures reflect the notices we were able to collect and classify. This data illustrates our monitored coverage, not a ranking of which places have the most dangerous water. Differences between states partly reflect how each publishes notices.
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Every factual claim on this page is drawn from primary public-health and regulatory guidance, or from our own advisory monitoring.
This site is an independent educational resource. It is not affiliated with the CDC, the EPA, or any water utility, and it does not replace the instructions your local water provider or health department gives you. Always follow your official notice.