Treating Water of Questionable Purity

If you are uncertain how pure your water source is, you should purify the water before consuming or storing it.

The treatments described below work only in situations where the water is unsafe because of the presence of bacteria or viruses. If you suspect the water is unsafe because of chemicals, oils, poisonous substances, sewage or other contaminants, do not use the water for drinking.

To purify your water, follow these steps.


Boiling is the safest way to purify water. Bring the water to a rolling boil for 3-5 minutes and let it cool before drinking.

Purifying With Bleach

If boiling is not possible, treat water by adding liquid household bleach, such as Clorox or Purex. Household bleach is typically between 5 percent and 6 percent chlorine. Avoid using bleaches that contain perfumes, dyes, or other additives. Be sure to read the label.

Place the water (filtered, if necessary) in a clean container. Add the amount of bleach listed in the table below. Mix thoroughly and allow to stand for at least 30 minutes before using (60 minutes if the water is cloudy or very cold).

Treating Water with a 5%-6% Liquid Chlorine Bleach Solution
Volume of Water
to be Treated
Treating Clear/
Cloudy Water
Bleach Solution to Add
Treating Very Cold
or Surface Water
Bleach Solution to Add
1 quart/1 liter 3 drops 5 drops
1/2 gallon/2 quarts/2 liters 5 drops 10 drops
1 gallon 1/8 teaspoon 1/4 teaspoon
5 gallons 1/2 teaspoon 1 teaspoon
10 gallons 1 teaspoon 2 teaspoon

For more information, see Purifying Water During an Emergency from the Washington State Department of Health.