Boiling water kills most bacteria and viruses, but not all contaminants
Boiling water for one minute at a rolling boil will kill most bacteria, viruses, and parasites that cause waterborne illness. This includes E. coli, salmonella, cholera, and hepatitis A. At higher elevations (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.
However, boiling does not remove chemical contaminants, heavy metals, or salt. If your water contains lead, pesticides, nitrates, or chlorine, boiling will not make it safe—and in some cases, boiling can concentrate these substances by evaporating the water around them. Boiling also does not remove sediment or cloudiness.
The safest approach is to know what is actually in your water before deciding whether boiling alone is enough. If you are dealing with a boil water notice from your local water utility, follow their specific instructions—they test the water and tell you exactly what threat you are protecting against.
Key Takeaways
- Boiling water for one minute kills bacteria, viruses, and parasites that cause common waterborne illness.
- Boiling does not remove chemicals, heavy metals, salt, or sediment from water.
- At elevations above 6,500 feet, boil for three minutes because water boils at a lower temperature.
- A boil water notice from your utility tells you what specific threat exists and how long to boil.
- If you suspect chemical contamination, boiling alone is not sufficient—you will need a filter rated for that contaminant.
When a boil water notice is issued
A boil water notice comes from your city or county water department when they detect bacteria or parasites in the water supply. This usually happens after a main breaks, a treatment plant fails, or contamination is found during routine testing. The notice tells you to boil tap water before drinking, cooking, or brushing teeth.
Follow the notice exactly: boil for the time specified (usually one minute, three minutes at high elevation), let the water cool, and store it in a clean container. Once the water utility lifts the notice—which they announce publicly and often post on their website—you can stop boiling. Do not assume the notice is lifted just because you have not heard about it; contact your water department or check their website to confirm.
What boiling removes versus what it does not
| Contaminant Type | Boiling Removes It | Notes |
|---|---|---|
| Bacteria (E. coli, salmonella, cholera) | Yes | One minute at rolling boil; three minutes above 6,500 feet |
| Viruses (hepatitis A, norovirus) | Yes | Same timing as bacteria |
| Parasites (giardia, cryptosporidium) | Yes | Same timing as bacteria |
| Lead | No | Boiling can concentrate lead by evaporating water |
| Pesticides and herbicides | No | Requires activated carbon filter |
| Nitrates | No | Requires reverse osmosis or ion exchange filter |
| Chlorine | Partially | Some chlorine evaporates; activated carbon removes more |
| Salt and minerals | No | Boiling concentrates these as water evaporates |
| Sediment and cloudiness | No | Requires settling or mechanical filtration |
How to boil water correctly
Fill a pot with tap water and bring it to a rolling boil—large bubbles breaking the surface continuously, not just steam rising. Once it reaches a rolling boil, start your timer. Boil for one minute (or three minutes if you are above 6,500 feet). You do not need to boil longer; the heat kills pathogens quickly once the water reaches boiling temperature.
Turn off the heat and let the water cool before drinking or using it. You can speed cooling by pouring the boiled water into a clean container and setting it in a sink of cold water, or straightforward leaving it on the counter. Store cooled boiled water in a clean, covered container in the refrigerator; it will keep for three days. If you are boiling water for cooking, you can use it while it is still hot.
Do not rely on the water "looking clean" to know when boiling is done. Cloudiness or color does not tell you whether pathogens are dead. Set a timer and follow the one-minute (or three-minute) rule every time.
When boiling is not enough
If your water contains lead, pesticides, nitrates, or other chemicals, boiling will not remove them. In fact, boiling can make some problems worse: as water evaporates during boiling, the concentration of dissolved minerals and chemicals increases in what remains. If you suspect chemical contamination, contact your local water utility and ask for a water quality report, or have your water tested by a certified lab.
If testing shows chemical contamination, you will need a filter designed for that specific contaminant. Activated carbon filters remove chlorine and some pesticides. Reverse osmosis systems remove nitrates, salt, and many chemicals. Ion exchange filters soften water and remove certain minerals. A straightforward pitcher filter (like Brita) removes some chlorine and improves taste, but does not remove bacteria, viruses, lead, or most chemicals—boiling is still necessary for pathogen removal if you use only a pitcher filter.
Boiling water for cooking and cleaning
If a boil water notice is in effect, boil water before using it for cooking pasta, rice, or other foods that absorb water. Boil water before using it to wash vegetables or prepare ice. You do not need to boil water for washing dishes or hands—regular tap water is fine for these purposes during a boil water notice, because the soap and friction remove pathogens.
If you have a dishwasher, check whether it reaches high enough temperatures to kill pathogens. Most modern dishwashers heat water to 140°F or higher, which is hot enough, but older machines may not. When in doubt, hand-wash dishes with boiled water during a notice.
Frequently Asked Questions
Does boiling remove chlorine from tap water?
Boiling removes some chlorine because it evaporates as the water heats, but not all of it. If you want to remove chlorine taste and smell completely, let boiled water sit uncovered for 24 hours (chlorine continues to evaporate), or use an activated carbon filter. Boiling does not remove chlorine compounds that are added to some water systems as a longer-lasting disinfectant.
Is it safe to boil water in a microwave?
Yes, but be careful. Microwave-heated water can reach boiling temperature without showing visible bubbles, which means you might not realize it is hot enough. Heat water in the microwave for two to three minutes on high power, then carefully remove it and let it sit for one minute before using. The one-minute boil time still applies—the water must be at a rolling boil temperature, not just hot.
How long can I store boiled water?
Store cooled boiled water in a clean, covered container in the refrigerator for up to three days. If you store it at room temperature, use it within 24 hours. If the water develops an odor or cloudiness, discard it and boil fresh water. Label the container with the date you boiled it so you do not lose track.
Do I need to boil bottled water?
Bottled water is regulated by the FDA and does not require boiling unless there is a specific contamination notice from the bottler. However, if you are using bottled water during a boil water notice and the notice specifies all water sources, check the bottler's website or call them to confirm the water is safe. Some people boil bottled water anyway for extra caution, which is fine but not necessary under normal circumstances.
What if I forget to boil water during a notice—is it dangerous?
Drinking unboiled water during a boil water notice carries risk, but it does not may provide illness. The risk depends on the specific pathogen present, the amount of contaminated water you drank, and your immune system. If you accidentally drank unboiled water, monitor yourself for symptoms like diarrhea, nausea, or stomach cramps over the next few days. If symptoms appear, contact your doctor and mention the boil water notice. Most people recover without treatment, but some illnesses require medical care.