Boiling water kills most bacteria and viruses, but not all contaminants
Boiling water for one minute at a rolling boil will kill most bacteria and viruses that cause waterborne illness — including E. coli, salmonella, cholera, and hepatitis A. At higher altitudes (above 6,500 feet), boil for three minutes instead, because water boils at a lower temperature and takes longer to reach the heat needed to kill pathogens.
Boiling does not remove chemical contaminants like lead, pesticides, nitrates, or chlorine. Heat actually concentrates some chemicals by evaporating water and leaving the dissolved substances behind. If your water contains lead from old pipes or chemical runoff from nearby industry, boiling makes the problem worse, not better.
Boiling also does not remove sediment, rust, or cloudiness. If your water looks discolored or tastes metallic, boiling will not clear it. You would need to filter the water first, then boil it if you are concerned about pathogens.
Key Takeaways
- Boiling kills bacteria and viruses that cause diarrhea and food poisoning, but only if you maintain a rolling boil for at least one minute.
- Boiling does not remove lead, pesticides, or other chemicals — it can concentrate them by reducing the water volume.
- If your water is cloudy, discolored, or has a chemical smell, boiling alone will not make it safe to drink.
- At altitudes above 6,500 feet, boil for three minutes instead of one to account for lower boiling temperatures.
When boiling is the right choice
Boiling is the correct response if you have been notified of a boil water advisory by your local health department or water utility. These advisories are issued after water main breaks, flooding, or contamination events where bacteria or viruses may have entered the system. The advisory will specify how long to boil — usually one minute — and which neighborhoods are affected.
Boiling also works if you are traveling to a country where tap water carries pathogens unfamiliar to your immune system, or if you are using water from a well, stream, or other untreated source. In these cases, the risk is biological, not chemical, and heat will address it.
If you are camping or hiking and have no way to filter water, boiling is your best option to reduce the risk of giardia and cryptosporidium from animal waste upstream. Bring the water to a rolling boil and let it cool before drinking.
When boiling is not enough
If your water comes from an old building with lead pipes or solder, boiling will not remove the lead. Lead dissolves in water and stays dissolved even at high temperatures. The only way to remove it is through a water filter certified for lead removal — usually a pitcher filter, faucet-mounted filter, or whole-house system. Boiling actually concentrates lead by reducing the total volume of water.
If you live near agricultural land, a factory, or a landfill, your water may contain pesticides, fertilizer runoff, or industrial chemicals. Boiling does not remove these. You would need a filter rated for the specific contaminant — activated carbon filters work for some chemicals but not others. Contact your local water utility or health department to find out what is in your water before choosing a filter.
If your water smells like rotten eggs, gasoline, or chemicals, or if it tastes salty or bitter, boiling will not fix it. These are signs of chemical or mineral contamination that requires filtration or, in some cases, a different water source.
How to boil water correctly
Fill a pot with tap water and place it on the stove over high heat. Wait for the water to reach a rolling boil — large bubbles breaking the surface continuously, not just small bubbles forming at the bottom. Once it reaches a rolling boil, set a timer for one minute (or three minutes if you are above 6,500 feet elevation).
After the time is up, turn off the heat and let the water cool to room temperature or refrigerate it. You can store boiled water in a clean, covered container in the refrigerator for up to three days. If you store it longer, bacteria can regrow.
If you are boiling water for drinking, you can also boil it in an electric kettle — just make sure it has an automatic shutoff so you know when it reaches a boil. Some kettles have a temperature setting; set it to 212°F (100°C) or the highest setting available.
Boiling versus filtering versus bottled water
Boiling is free if you have a stove and takes about 10 minutes from start to cool-down. It works for biological contaminants but not chemicals. Filtering costs between $20 and $200 upfront depending on the type, removes both some bacteria and some chemicals (depending on the filter), and requires replacement cartridges every few months. Bottled water costs money every time you buy it and creates plastic waste, but it is regulated by the FDA and tested for both pathogens and chemicals.
If you are under a boil water advisory, boiling is the fastest and cheapest response. If you are concerned about long-term water quality, a filter rated for your specific contaminants is usually the better choice. If you are traveling or in an emergency, bottled water is the safest option if boiling is not possible.
What happens if you drink unboiled contaminated water
If your water contains bacteria or viruses, you may develop symptoms within hours or days: diarrhea, nausea, vomiting, stomach cramps, or fever. Most cases resolve on their own within a few days, but young children, elderly people, and people with weakened immune systems can become seriously ill or dehydrated. If you develop severe symptoms or symptoms that last more than a few days, see a doctor.
If your water contains lead or other chemicals, you usually will not notice symptoms right away. Lead exposure over months or years can cause learning problems in children and high blood pressure in adults. Chemical contaminants like pesticides or nitrates may not cause when ready illness but can increase health risks over time. This is why testing your water and using a filter is important if you suspect chemical contamination.
How to know if your water is safe
If you are on a public water system, your water utility must provide a water quality report (called a Consumer Confidence Report) once a year. You can request it by phone or find it on the utility's website. The report lists what contaminants were found and whether they are at safe levels.
If you have a private well, you are responsible for testing it. Your local health department can tell you which labs are certified to test well water and what contaminants to test for. Testing costs between $100 and $300 depending on how many contaminants you check.
If you notice changes in your water — cloudiness, color, smell, or taste — contact your water utility right away. They can tell you whether it is a known issue and whether you should boil your water or use another source.
Frequently Asked Questions
Does boiling remove chlorine from tap water?
Boiling removes some chlorine because it is a gas that evaporates when water is heated. However, it does not remove all of it, and some chlorine may remain. If you want to remove chlorine completely, use an activated carbon filter or let water sit uncovered in the refrigerator for 24 hours, which allows chlorine to evaporate slowly.
Can I boil water in a microwave instead of on the stove?
Yes, but it is less reliable. Microwave heating can be uneven, and water may not reach a true rolling boil. If you use a microwave, heat the water for several minutes, then carefully remove the container and check that large bubbles are breaking the surface. Stove boiling is faster and more certain.
How long does boiled water stay safe to drink?
Boiled water stays safe as long as it remains covered and stored in a clean container. Once it cools, bacteria can begin to regrow. Store boiled water in the refrigerator in a sealed container for up to three days. If you leave it at room temperature, use it within a few hours.
What if I live at high altitude — how long should I boil?
At elevations above 6,500 feet, water boils at a lower temperature because air pressure is lower. Boil for three minutes instead of one to make sure pathogens are killed. If you are unsure of your elevation, check online or ask your local health department.
Does boiling water remove fluoride?
No. Fluoride does not evaporate when water is heated, so boiling does not remove it. If you want to remove fluoride, you need a filter specifically rated for fluoride removal, such as a reverse osmosis system or a specialized pitcher filter.