Does Boiling Water Kill Bacteria?

When your tap water seems questionable, boiling it is often the first solution that comes to mind. But does boiling water really make it safe to drink? The short answer is yes—boiling water is one of the simplest and most reliable methods of home water disinfection.

Access to safe drinking water is essential for maintaining good health, yet millions of people worldwide still face risks from waterborne bacteria and other contaminants. According to the World Health Organization (WHO), roughly one million people die each year from diseases linked to unsafe drinking water, poor sanitation, and inadequate hygiene. In the United States, over seven million people are affected by waterborne diseases each year, according to the Centers for Disease Control and Prevention (CDC).

One of the simplest and most effective ways to protect yourself from waterborne microorganisms is by boiling your water. This guide will walk you through how the boiling process works, best practices for storing boiled water safely, and how to tell if previously boiled water is still safe to drink.

How Boiling Water Kills Bacteria

Boiling water neutralizes most harmful microorganisms through heat. According to the New York State Department of Health, high temperatures denature (break down) the proteins in bacteria, protozoa, and viruses, stopping them from reproducing and ultimately killing them.

However, the health department clarifies that while this method is effective, it is not the same as full sterilization, as it doesn’t remove every organism in the water. Instead, it’s similar to pasteurization (the process that often treats milk), destroying about 99.99% of bacteria and other pathogens that can make people sick.

There are several common types of each of these water contaminants that can be killed through boiling. Some examples include:

• Bacteria: E. coli, Salmonella, and Shigella.
• Protozoa: Amoebae, Cryptosporidium, and Giardia.
• Viruses: Hepatitis A, hepatitis E, and rotavirus.

How Long Should You Boil Water?

The boiling point of water varies depending on the altitude. At sea level, water boils at 212°F. This temperature is what denatures the bacterial proteins, making the water safer to drink. However, the boiling point of water decreases as altitude increases. For roughly every 500 feet above sea level, the boiling point drops by about 1°F.

For example, in Leadville, Colorado(located over 10,000 feet above sea level), the boiling point is only 194°F.

Because of this, the CDC states that water must be brought to a rolling boil for at least one minute to kill germs at lower elevations. A rolling boil means the bubbles are constantly rising to the top and popping, allowing the water to move continuously. However, for people at elevations above 6,500 feet (where water boils at 200.3°F), the CDC advises keeping the water at a boil for three minutes.

Benefits of Boiling Water for Disinfection

Boiling water to make it safe to drink is not something you will commonly have to do in the U.S. However, if you go camping, an emergency occurs, or your area is under a water boil advisory, it may become necessary. Boiling water is an effective solution for killing waterborne germs without the need for chemicals or reliance on commercial bottled water.

A boil-water advisory is a notice issued by local authorities to residents when municipal drinking water is contaminated, such as after flooding, pipe damage, or sewage leaks. These notices will vary in length and direction, but it is essential to follow them, as the time required to boil water depends on where you live. If your tap water is brown, that does not necessarily indicate a need for boiling your water. This most commonly happens when sediment enters the water. Let your tap run slowly, on cold, for a few minutes. If it doesn’t clear up after that, call your water company for further instructions.

Limitations of Boiling Water

While boiling water is one of the simplest and most effective disinfection methods, it isn’t a perfect solution. Keep these limitations in mind:

• Affects taste: Sometimes boiled water can taste flat due to the container it is stored in, and because the gases in the water are released during the boiling process, which alters the taste.
• It doesn’t remove chemicals, heavy metals, or certain toxins: Boiling water is not a practical solution for removing all other contaminants. It cannot break down things like cyanotoxins, lead, or PFAS.
• Time- and energy-consuming: Boiling water requires time and energy, making it less practical than using a water filtration system for everyday use.
• Susceptible to recontamination: Unclean hands, utensils, or storage vessels can easily recontaminate boiled water. It is essential to only handle water with sanitized items or hands to avoid needing to redo the process.

Because of these limitations, many homeowners pair boiling with filtration or purification systems, such as reverse osmosis or activated carbon filters, for long-term protection and better-tasting water.

Boiling Water vs. Other Purification Methods

When it comes to removing bacteria, boiling water is highly effective. However, it isn’t always the most practical way to get clean water. This chart breaks down which methods are best for different contaminants and how to best use them.

Practical Tips for Safe Boiling and Storage

First and foremost, you need to have a clean and sanitized vessel to hold the boiled water. The container should be made from ceramic, durable plastic, or metal and washed thoroughly with hot and soapy water and rinsed well. Then, mix one teaspoon of bleach with one quart of water. Put the mixture into the container and shake for about 30 seconds before dumping it out. Then let it air dry completely or rinse with clean water before use. If the container isn’t completely clean, the water can become contaminated.

After boiling the water, ensure it is completely cooled before sealing it in a BPA-free container. Properly stored boiled water is safe and consumable for up to six months.

If the water becomes cloudy, develops an odor, or tastes off, discard it immediately. To help prevent this, store containers in a cool, dark place away from direct sunlight or heat sources. And keep them well away from gasoline, paint, or other chemicals, as vapors can leach into the water.

In short, be sure to:

• Use sterilized, BPA-free containers
• Store in a cool, dark place
• Keep away from fuel, chemicals, and sunlight
• Discard water that looks, tastes, or smells off

Key Takeaways on Boiling Water for Home Safety

Although boiling cannot completely purify the water, it is effective in killing up to 99.99% of germs, including bacteria, protozoa, and viruses. It is essential during an emergency or when a water boil order is in effect due to an issue with the water supply.

Boiling water is not an everyday solution for clean drinking water, but it’s a reliable backup option when you need it. For everyday protection, consider regular water testing and adding a whole-home UV filter as a part of your whole-home filtration system. At Leaf Home, we offer free water testing and tailored solutions to keep your family hydrated and healthy. But for those in-between, urgent moments, boiling is your best bet for safer water.

Frequently Asked Questions

Will boiling water remove chemicals or heavy metals?

Boiling will not remove chemicals or heavy metals from the water. The best way to help reduce those contaminants is with a water filter or purification system such as those offered by Leaf Home.

Can I boil water to make it safe after a storm or boil advisory?

Yes. Boiling water during a boil advisory or after a natural disaster or storm is important in protecting you against harmful germs. Always follow your local boil-water notice guidelines. These advisories are issued by public health authorities for a reason—they specify how long to boil, when it’s safe to stop, and any additional steps needed for your area. Even if your water looks clear, continue boiling until officials confirm that it’s safe to drink again.

Is boiled water safe for infants or immunocompromised individuals?

Boiled water is usually safe for infants and immunocompromised people as long as it is cooled and stored correctly. However, safety depends on the health of the individual and the type of contamination—boiling kills bacteria, viruses, and parasites, but it does not remove chemicals or heavy metals. The CDC’s boiling water guidelines apply to the general public, including infants and those with compromised immunity—but it doesn’t guarantee safety in all contamination scenarios. In cases of severe contamination, consult your local health department before using boiled water.

And remember that after a boil water advisory is lifted, plumbing in buildings might still have pathogens in pipes; systems must be flushed and disinfected.

How long can I store boiled water before it needs reboiling?

You can safely store boiled water for up to six months in a clean, tightly sealed container made of ceramic, durable plastic, or stainless steel. Keep it in a cool, dark place away from chemicals or direct sunlight. If the water becomes cloudy, smells unusual, or tastes off, discard it and replace it with freshly boiled water.