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Emergency prep

Safe water, step by step. Bleach drops and boil times that match the EPA.

Check the strength on your bleach bottle, then add 6 drops of 8.25% bleach or 8 drops of 6% per gallon and wait 30 minutes. Or boil it for 1 minute.
Bleach and boil calculatorWhat it can't fix

Figures checked against EPA and CDC.

Bleach and boil calculator

Bleach: how many drops

1. Strength on the bottle (sodium hypochlorite)

Add to 1 gallon

6 drops

of regular, unscented 8.25% bleach.

Stir and wait 30 minutes. It should smell slightly of chlorine. If not, add the same dose again and wait 15 more minutes.

Boiling: how long

Rolling boil for

1 minute

CDC and EPA agree at this elevation.

Let it cool on its own, then store it in clean, covered containers.

EPA bleach table

Regular, unscented chlorine bleach. Read the label: it should list 6% or 8.25% sodium hypochlorite. Copied from the EPA page, updated February 24, 2026.

EPA bleach doses for disinfecting drinking water by volume and bleach strength
Water6% bleach8.25% bleach
1 quart or liter2 drops2 drops
1 gallon8 drops6 drops
2 gallons16 drops (1/4 tsp)12 drops (1/8 teaspoon)
4 gallons1/3 teaspoon1/4 teaspoon
8 gallons2/3 teaspoon1/2 teaspoon
  1. If the water is cloudy, let it settle, then pour it through a clean cloth, paper towel or coffee filter.
  2. Add the dose from the table. Double it for cloudy, colored or very cold water.
  3. Stir and let it stand 30 minutes.
  4. It should smell slightly of chlorine. If not, repeat the dose and wait 15 more minutes.
  5. Store it in clean containers with covers.

CDC uses one figure for all bleach between 5% and 9%: 8 drops per gallon, 40 drops for 5 gallons. For 1% bleach, CDC says 40drops per gallon. Where the two differ for 8.25% bleach, we show EPA's strength-specific figure.

What boiling, bleach and filters can and cannot do

What each water treatment method handles
MethodHandlesDoes not handle
BoilingGerms: CDC calls it the best way to kill germs in waterHeavy metals, salts, most chemicals, fuel
BleachViruses and bacteria (CDC)May not kill parasites such as Cryptosporidium (CDC); chemicals, fuel
Chlorine dioxide tabletsGerms including Cryptosporidium, when used as directed (CDC)Chemicals, fuel
FilterMost remove parasites; parasites need 1 micron or smaller, bacteria 0.3 micron or smaller (CDC)Viruses, and bacteria for most filters (CDC); chemicals unless certified for them
Floodwater and anything that smells of fuel: do not drink it. CDC says you cannot make water containing fuel, toxic chemicals or radioactive material safe by boiling or disinfecting it. Use stored or bottled water and call your health department.

Buying a filter? A purifier is built for water of unknown quality and handles viruses too. See emergency water filters ranked by certification, and plan how much to keep on hand with the water storage calculator.

Frequently asked questions

How much bleach do I add to a gallon of water?

It depends on the strength on the label. EPA: 8 drops of 6% bleach or 6 drops of 8.25% bleach per gallon, using regular unscented bleach. Double it if the water is cloudy, colored or very cold. Stir, wait 30 minutes, and check for a slight chlorine smell.

How long do you boil water to make it safe?

Bring it to a rolling boil for 1 minute. CDC says 3 minutes above 6,500 feet; EPA says 3 minutes above 5,000 feet. If you live between the two, boiling for 3 minutes satisfies both.

Does boiling or bleach remove chemicals?

No. EPA says boiling or disinfection will not destroy heavy metals, salts and most other chemicals. CDC says water containing fuel, toxic chemicals or radioactive material cannot be made safe by boiling or disinfecting. Use stored or bottled water instead and contact your health department.

Can I use scented or color-safe bleach?

No. EPA says to use only regular, unscented chlorine bleach suitable for disinfection, and not scented, color-safe bleach or bleach with added cleaners. Use bleach stored at room temperature for less than 1 year.

Is a water filter enough on its own?

Not for water of unknown quality. CDC says most portable filters remove parasites but not viruses or bacteria, and recommends adding a chemical disinfectant after filtering. To remove bacteria a filter needs a pore size of 0.3 micron or smaller; for parasites, 1 micron or smaller. A purifier made to the EPA purifier standard is designed to handle viruses too.

What about iodine or purification tablets?

EPA: 5 drops of 2% tincture of iodine per quart, 10 if cloudy, then wait 30 minutes. For tablets, follow the label. CDC says iodine and chlorine do not kill Cryptosporidium (chlorine dioxide does), and that pregnant people and people with thyroid problems should not drink iodine-treated water.

General information, not medical advice. If your utility issues a boil-water notice or other instructions, follow them. See our disclaimer.

Sources

  1. US EPA, Emergency Disinfection of Drinking Water — bleach table by strength, double for cloudy or cold, 30 + 15 minutes, iodine, 3 minutes above 5,000 ft; updated Feb 24 2026
  2. CDC, Making Water Safe in an Emergency — 1 minute rolling boil, 3 minutes above 6,500 ft; 5-9% and 1% bleach; filters and viruses; chemicals cannot be removed
  3. CDC, A Guide to Water Filters (Cryptosporidium) — pore sizes and NSF 53 or 58 cyst reduction

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Photo: Devon MacKay on Unsplash (Unsplash License).