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How To Treat Water with Chlorine


Updated January 23, 2014

Giardia lamblia and Cryptosporidium are often found in rivers and lakes. In a disaster, if boiling water is not possible, unscented chlorine bleach can be used to treat it.

Always choose flowing water sources (rivers and streams) over stagnant water (lakes and ponds) and treat before using. Well water is usually safe, but can become contaminated during a flood. Don't consume well water after a natural disaster unless instructed to do so by authorities.

Unless water has been deemed safe by authorities, it must be disinfected before drinking, cooking, making prepared drinks (such as baby formula), or brushing teeth.

Difficulty: Easy

Time Required: 2-3 Hours

Here's How:

  1. Filter cloudy water through clean cloths or coffee filters.


  2. Let water sit for an hour or two after filtering to allow any sediment to settle. Pour the clear water off the top into another container. Be careful not to dump the sediment into the new container.


  3. Use non-scented chlorine bleach and determine the percentage of chlorine by looking at the label. Use a dropper to add the chlorine to the water:
    • 1%: 10 drops per quart/liter - 40 per gallon
    • 4-6%: 2 drops per quart/liter - 8 per gallon
      (8 drops is about 1/8 teaspoon)
    • 7-10%: 1 drops per quart/liter - 4 per gallon
    Double the amount of chlorine for murky water, cloudy water, or extremely cold water.


  4. Stir the water thoroughly and let it stand.


  5. Check the water after 30 minutes. The water should have a slight chlorine smell. If it doesn't, repeat steps 3 and 4 again and let it sit for 15 more minutes. For water that has too strong of a chlorine taste, let it stand open for a few hours (without a lid) or pour it back and forth between two clean containers.


  6. Put the treated water into clean containers with lids.



  1. If bleach label contains directions for disinfecting water, follow the manufacturer's directions.
  2. Chemical treatment works better in warm water.
  3. Never use non-chlorine bleach or scented bleach to treat water.
  4. If the strength of the bleach is unknown, use 10 drops per quart. To use granular calcium hypochlorite instead of liquid bleach, make a stock chlorine solution by mixing one heaping teaspoon (about 1/4 ounce) with two gallons water. Disinfect water by mixing one part stock chlorine solution to 100 parts water.


    "Emergency disinfection of drinking water." 28 Nov 2006. Ground water and drinking water. US EPA. 27 Nov 2007.

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