Boiling is better than bleaching, but it will still do in a pinch—provided you follow the right precautions
Boil Water Advisory Says Add Bleach — Is It Really Safe? Experts Weigh In
Published on Apr. 17, 2025
My most memorable experience with a boil water advisory was when a landslide damaged the main water line to my mountain village, and we were without clean drinking water for more than four days. However, unlike the advice in some regions, chlorine-based disinfection methods were not mentioned. If, like me, you are wondering how you can use bleach to disinfect drinking water when boiling is not an option, read on so you are well-informed during an emergency.
I spoke to two water safety experts to understand when and why adding bleach to drinking water is appropriate and what the necessary precautions are.
What Is a Boil Water Advisory and Why Are They Issued?
Local public health or water authorities issue boil water advisories when drinking water is at risk of being contaminated with harmful pathogenic microorganisms, such as bacteria, viruses or illness-causing protozoan parasites, like Giardia.
Elena N. Naumova, PhD, is the Chair of the Division of Nutrition Data Science and a Professor at the Friedman School at Tufts University. She explains that a sudden loss of water pressure, water mains breaks and power outages or malfunctioning equipment in treatment plants are common reasons for a boil water advisory. “In some cases, routine water testing detects the presence of pathogens like E.Coli or coliform bacteria,” she says. “Heavy rains, flooding, or natural disasters can overwhelm water treatment systems and introduce contaminants into the supply.”
The Advisory informs the public that water must be boiled to be safe for drinking. “Boiling water is an effective way to kill most disease-causing organisms, including bacteria, viruses, and protozoa,” Naumova says. The heat from boiling damages the proteins and membranes of these pathogens, leading to their destruction.
How to Properly Boil Water During an Advisory
It’s not enough to wait for bubbles to form when heating water during a boil water advisory. You must bring the water to a rolling boil and keep it there for at least one minute. While most bacteria and viruses die off within seconds of temperatures between 70°C and 85°C, protozoa with protective cysts need higher sustained temperatures to kill them off.
Aria Amirbahman, the chair of the Civil Engineering Department and the Sukhmander Singh Endowed Professor at Santa Clara University, explains that boiling water for one minute at 100°C (212°F) is generally sufficient for disinfection, as the process leads to protein denaturation and, in some cases, the disruption of microbial cell walls. “However, to ensure safety—particularly at higher elevations where water boils at a lower temperature—it is advisable to boil water for up to five minutes,” he says.
Disinfecting Water with Bleach (When Boiling Isn’t an Option)
Disinfecting water with bleach in an emergency is not as drastic as it sounds, provided you follow the correct guidelines and precautions.
Is disinfecting water with bleach really safe?
You can disinfect water with bleach as an emergency water treatment strategy when boiling isn’t possible. This can be particularly helpful if you have a power outage. However, always use the right kind of bleach and the right amount.
“Liquid bleach, which contains sodium hypochlorite, disinfects water by oxidizing and destroying the cell membranes of microorganisms,” Amirbahman explains. “For emergency disinfection, it is generally recommended to add 8 drops of household bleach per gallon of clear water, with a few additional drops if the water is turbid [has a cloudy appearance],” he says.
However, adding chlorine to your water long-term or more than the recommended amount is not advised, as this can lead to toxic overexposure. “Drinking heavily chlorinated water can irritate the mouth, throat, and stomach, and may cause nausea or vomiting, especially in children or people with sensitive stomachs,” Naumova says.
How much bleach is too much for water purification?
It is not recommended to use more than 16 drops of household bleach (containing 5% to 6% sodium hypochlorite) per gallon of water. Naumova explains that the general guidance is to add 8 drops of bleach to clear water and wait 30 minutes before drinking. “The water should have a slight chlorine smell,” she says. “If not, repeat the dose and wait another 15 minutes.”
If the water is cloudy (turbid), the recommendation is to add 16 drops per gallon of water and wait 30 minutes before drinking. Naumova recommends filtering cloudy water through a cloth or coffee filter first, as this removes any larger particles.
Safety precautions
While bleach is a powerful water disinfectant, using it does have risks, and that’s why boiling is a better option when it’s available.
Only use plain, unscented household bleach, and take care when handling this skin and eye irritant. “Many household bleaches are scented, splashless, or concentrated—these varieties often contain additives like detergents, perfumes, or thickeners that are harmful or toxic if ingested,” Naumova says.
It’s also important to note that bleach doesn’t reliably kill all protozoan parasites with resistant outer shells, such as chlorine-resistant Cryptosporidium.
Amirbahman also points out that bleach loses effectiveness over time, particularly when exposed to heat and sunlight. He recommends replacing bleach bottles every three months.
Other Water Purification Methods
Iodine tablets and special water filtration systems are common alternatives to boiling or bleach for purifying drinking water. However, Amirbahman points out that iodine tablets are not recommended for long-term use, and filtration membranes may not effectively remove very small microorganisms, such as viruses, so these methods are best used in combination.
Naumova recommends only selecting filters specifically labeled to meet standards for microbial removal (such as NSF/ANSI 53 or 58). She also points out that filters require regular maintenance and replacement to remain effective.
“Portable UV sanitizers, such as SteriPEN, are effective against most microorganisms, including Giardia and Cryptosporidium, but UV light is most effective when the water is clear and free of turbidity,” Amirbahman says. “Solar disinfection, which involves exposing water in a clear glass or plastic bottle to direct sunlight for a full day, is another effective method, provided the water is not turbid.”
Naumova also recommends using emergency water purification products in order of priority, starting with boiling (if possible), then bleaching (if correctly dosed).
What Not to Do During a Boil Water Advisory
Don’t rely on your kettle to purify your water during a Boil Water Advisory. Naumova cautions that modern electric kettles often shut off automatically, meaning they may not achieve a rolling boil and temperatures required to kill off all harmful organisms.
Also, avoid using untreated water to brush your teeth or rinse your fruit and veggies, as this also exposes you to the risk of ingesting problematic pathogens.
Frequently Asked Questions
How long do boil water advisories last?
Boil water advisories typically last 24 to 48 hours. However, they could last several days or longer if a major incident affects the nearby water treatment plant.
Can I use bottled water instead of boiling?
Using bottled water instead of boiling during a boil water advisory is safe. Having a small supply of bottled water on hand for this type of emergency can be helpful.
Does Brita filter remove bacteria during an advisory?
A standard Brita water filter removes some taste and odor-impacting impurities from water. However, only specialized filters will remove bacteria and other microbial contaminants that are a concern during a boil water advisory.
About the Experts
- Aria Amirbahman is the chair of the Civil Engineering Department and the Sukhmander Singh Endowed Professor at Santa Clara University. His research interests are aquatic chemistry, contaminant transport, and water treatment; email interview, Apr. 14, 2025
- Elena N. Naumova, PhD, is a Professor in the Nutrition Epidemiology and Data Science Division of the Friedman School of Nutrition Science and Policy at Tufts University. She is also an AAAS Fellow with the Societal Impacts of Science and Engineering and Editor-in-Chief of the Journal of Public Health Policy, Springer Nature; email interview, Apr. 11, 2025.
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