PrepWater purification calculator: how much bleach per gallon
Enter how much water you have and the strength on your bleach label. You'll get the dose in drops and mL, from EPA and CDC figures. If you can boil the water, do that instead.
Your water and bleach
If the label has its own instructions for disinfecting water, follow those instead.
Bleach dose table
For clear water, as printed by EPA and CDC. EPA doesn't print mL, so the 6% column uses CDC's mL, and the 8.25% column has none. EPA doesn't print 5 gallons, so those two figures are its per-gallon dose multiplied: 40 drops at 6% matches CDC.
| Water | 6% (EPA) | 8.25% (EPA) | Other 5–9% (CDC) |
|---|---|---|---|
| 1 quart or liter | 2 drops, 0.1 mL | 2 drops | 2 drops, 0.1 mL |
| 1 gallon | 8 drops, 0.5 mL | 6 drops | 8 drops, 0.5 mL |
| 2 gallons | 16 drops, 1 mL | 12 drops | 16 drops, 1 mL |
| 5 gallons | 40 drops, 2.5 mL | 30 drops | 40 drops, 2.5 mL |
Cloudy, colored or very cold water: double it
| Water | 6% (EPA) | 8.25% (EPA) | Other 5–9% (CDC) |
|---|---|---|---|
| 1 quart or liter | 4 drops, 0.2 mL | 4 drops | 4 drops, 0.2 mL |
| 1 gallon | 16 drops, 1 mL | 12 drops | 16 drops, 1 mL |
| 2 gallons | 32 drops, 2 mL | 24 drops | 32 drops, 2 mL |
| 5 gallons | 80 drops, 5 mL | 60 drops | 80 drops, 5 mL |
Boil it, if you can
- If it's cloudy, let it settle, then filter it through a clean cloth, paper towel or coffee filter.
- Bring it to a rolling boil for at least 1 minute. Above 5,000 feet, boil for 3 minutes.
- Let it cool naturally. Store it in clean containers with covers.
Never use a camp stove or charcoal grill indoors to boil water, because of carbon monoxide (CDC). To improve the taste, EPA says to add a pinch of salt per quart or pour it between clean containers.
Which bleach to use
- ✓ USE Regular, unscented liquid chlorine bleach, labeled as suitable for disinfection and sanitization.
- ✓ USE Fresh bleach, or bleach kept at room temperature for less than a year.
- × NOT Scented bleach.
- × NOT Color-safe bleach.
- × NOT Bleach with added cleaners.
Strength is the percent of sodium hypochlorite on the label. CDC says it's typically 5% to 9% in the US. If yours isn't on the label, this tool can't give you a dose.
When not to use the water
- × NOT It has fuel, toxic chemicals or radioactive material in it, or might. Boiling and disinfecting won't make it safe. Use bottled water or another source, and call your health department.
- × NOT It has floating material, a dark color or a questionable odor.
- × NOT Local officials have said not to use it. Follow their notice, not this page.
Boiling and bleach kill most germs. They don't remove heavy metals, salts or most other chemicals. If a private well was flooded, disinfect and test it, and ask your state or local health department.
Water you treat this way is for drinking, cooking, prepared drinks, washing dishes and brushing teeth. CDC says portable filters don't remove viruses, so add a disinfectant after filtering. For tablets, follow the label, since strengths vary. Iodine and chlorine tablets don't kill Cryptosporidium.
From preppantry.app. Checked 2 November 2026. Independent tool, not official advice.
How it works
We use EPA's table for 6% and 8.25% bleach, and CDC's for any other strength from 5% to 9%. For cloudy, colored or very cold water, both agencies say to double the amount, so we do.
What's printed and what's worked out: EPA prints drops for 1 quart or liter, 1 gallon and 2 gallons. CDC prints drops and mL for 1 quart or liter, 1 gallon and 5 gallons. For other amounts, we multiply the per-gallon dose, and the result says so. We stop at 8 gallons, where EPA's table ends.
Why there are no teaspoons: EPA's teaspoon figures don't line up with its drops. It gives 16 drops or ¼ teaspoon for 2 gallons, then ⅓ teaspoon for 4 gallons, when twice the amount would be ½. So this page uses drops and mL only.
Why mL looks different at 8.25%: EPA gives this strength in drops only. CDC gives one dose for all bleach from 5% to 9%, in drops and mL, and at 8.25% that's a little more than EPA's. We show EPA's drops first, and CDC's figure beside it for anyone measuring in mL. For 6% bleach, EPA's drops match CDC's, so we use CDC's mL.
Boiling at altitude: EPA says to boil for 3 minutes above 5,000 feet, and CDC says above 6,500 feet. We use the lower one.
Common questions
How much bleach per gallon of water?
EPA says 8 drops of 6% bleach or 6 drops of 8.25% bleach per gallon of clear water. Double it if the water is cloudy, colored or very cold. Stir, then let it stand for 30 minutes.
What kind of bleach can I use?
Regular, unscented liquid chlorine bleach whose label says it's suitable for disinfection and sanitization. Don't use scented or color-safe bleach, or bleach with added cleaners. EPA says it should be fresh, or stored at room temperature for less than a year.
What if the water doesn't smell of chlorine afterward?
EPA says to repeat the dose and let it stand for another 15 minutes. Ready.gov adds that if it still doesn't smell of chlorine, you should discard it and find another source.
How long should I boil water?
Bring it to a rolling boil for at least 1 minute, or 3 minutes above 5,000 feet. Let it cool naturally and store it in clean, covered containers.
Does boiling or bleach make all water safe?
No. They kill germs. They don't remove heavy metals, salts or most other chemicals. CDC says water with fuel, toxic chemicals or radioactive material isn't made safe by boiling or disinfecting.
What if my bleach isn't 5% to 9%?
Check the label for instructions on disinfecting water and follow those. This tool gives no dose outside that range. CDC's page has a separate table for 1% bleach.
Sources
- US EPA: emergency disinfection of drinking water (updated 24 February 2026)
- CDC: making water safe in an emergency (19 September 2024)
- Ready.gov: water (last updated 22 February 2021)
- CDC: what to do in a power outage (carbon monoxide)
Checked on 2 November 2026. This is an independent tool and not official advice. See sources and method.