Sanitary water may be found in closed containers (C) Daniel FriedmanHow Much Water Disinfectant to Use to Purify or Sterilize Drinking Water

  • WATER DISINFECTANT QUANTITY - CONTENTS: How much bleach, chlorine, iodine, or other disinfectant to use to treat drinking water. How long to wait to drink water after adding a disinfection chemical or tablet. How water temperature affects the amount of disinfectant needed or the wait time for disinfection to be complete before drinking treated water. Increased water treatment time for very cold water. Increased water treatment time for cloudy water. How to treat, purify, or sterilize drinking water in an emergency
  • POST a QUESTION or READ FAQs about how much disinfectant (bleach or chlorine, iodine, etc) to use to disinfect drinking water

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This drinking water disinfection article gives the details of the amount of different types of disinfectant needed to treat drinking water - the disinfectant concentration needed to make water safe to drink.

We explain the increased treatment time or contact time needed depending on the actual chlorine concentration in different bleach products, the actual water temperature and depending on whether or not the treated water is cloudy.

This article series outlines methods to purify or sanitize drinking water in an emergency following a disaster such as an earthquake, flood, or hurricane.

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How Much Disinfectant to Use in Drinking Water?

Sanitary water may be found in closed containers (C) Daniel FriedmanArticle Contents:

The amount of disinfectant needed to purify water depends on how contaminated the water is to begin with. If you are using liquid iodine and have no better authoritative information, try a teaspoon of iodine per gallon of water. Other experts recommend:

  • Iodine in clear water: 5 drops of 2% tincture of iodine per quart of clear water
  • Iodine in cloudy water: 10 drops of 2% tincture of iodine per quart of cloudy water
  • Other water disinfectant products based on iodine: the label will indicate the number of capfuls of disinfectant to use per quart of water
  • Iodine tablets, such as PotableAqua™ - (50 tablets per bottle) two tablets treats a quart of water and are effective against Giardia lambia.

    Also see the U.S. Army field manual FM 21-10 Chapter 2: Individual Preventive Medicine Procedures where preferred and alternative methods of emergency drinking water purification using iodine are discussed:
  • Bleach for sterilizing drinking water: the number of drops of bleach to add per gallon of water depend on the percent concentration of the bleach product you are using. Let your bleached water stand for 30 minutes before using it. If the water does not have a slight "bleach" smell, repeat the dose and let the water stand for an additional 15 minutes. If you let the water stand longer the unpleasant bleach odor will dissipate completely.

    Definition of the EPA-recommended Superchlorination procedure for drinking water: the U.S. EPA recommends adding one teaspoon of chlorine bleach per ten gallons of drinking water in order to reach a chlorine concentration of 3.0 ppm in the drinking water. Use three teaspoons, or one tablespoon of chlorine bleach per 30 gallons of water to be treated.

    Watch out: not all bleach solutions provide the same concentration of chlorine, so just using one teaspoon of chlorine bleach per ten gallons may be unreliable. Use a chlorine test kit or swimming pool test kit (CHLORINE in WATER, HOW TO TEST FOR) to confirm that your superchlorinated drinking water has reached 3.0 ppm.

    Watch out: the concentration of chlorine in drinking water after bleach has been added will not remain constant. The concentration is highest immediately after the chlorine-based bleach has been added to the water. When treating a quantity of drinking water (such as in an RV holding tank) or other container, see "Wait Time & Water Temperature" (just below in this article) or else wait six hours before testing to determine if the chlorine concentration is at 3.0 ppm. That wait time also gives more contact time to permit the disinfectant action of the bleach to destroy the organisms that are its target.

    • 1% bleach: use 40 drops of bleach per gallon of drinking water
    • 2% to 6% bleach solution: use 8 drops of bleach per gallon of water
    • 7% to 10% bleach solution: use 4 drops of bleach per gallon of water
    • Unknown bleach concentration (presuming this is store-bought laundry bleach): use 10 drops of bleach per gallon of water.
    • WELL DISINFECTANT pH ADJUSTMENT may also be necessary for effective water disinfection.

The table below is derived from U.S. Army field manual FM 21-10 Chapter 2: Individual Preventive Medicine Procedures

Drops of Bleach to Be Added to a One Quart Canteen For Emergency Drinking Water
Available Chlorine Clear Water Cold or Cloudy Water
1% 10 20
4—6% 2 4
7--10% 1 2

Wait Time & Water Temperature when adding a disinfectant, before drinking water

  • Typical wait time before drinking treated water is at least 30 minutes from the time that the treatment tablet has become fully dissolved in the water. The necessary time could be longer.
  • Water temperature should be 65 degF or higher before treatment with bleach for best results. You may be able to warm your water by placing it in the sun. If the water is below 40 deg.F. you should double the wait time before consuming it.
  • Water temperature should be 68 degF or higher before treating it with iodine. Iodine is more effective than bleach in killing off Giardia contamination in water.
  • Be sure to read the instructions. Iodine, bleach (sodium hypochlorite), or other water disinfectants will require some wait time to permit the chemical to act on water bacteria before the water can be consumed.
  • Water Disinfectant Contact time: Using any chemical to sterilize water will require sufficient contact time between the chemical and the water before the water can be consumed. The chemical, bleach, or iodine, needs time to kill the microorganisms in the water.
  • If you have iodine tablets intended for purifying water, the tablet bottle label should indicate the number of tablets to use per gallon of water and also the length of time that you must let the water sit before drinking it.
  • If using liquid iodine to purify water, let the treated water sit for a day before using it to drink.
  • If your water supply is very cold you will need to increase the wait time for the chemical disinfectant to act before the water can be consumed.
  • If your water supply is cloudy you will need to increase the wait time for the chemical disinfectant to act before the water can be consumed. That's why experts recommend filtering the water with a clean cloth first if you can. In an emergency you might also be able to use clean coffee filters or even plain white paper towels.

Water Disinfection Does Not Remove All Contaminants

Municipal water supplies are generally safe as their water treatment efficacy is monitored regularly as required by federal regulations. But private water supplies may be unsafe and are almost certainly unsafe after disasters such as flooding.

Watch out: as we report throughout this article series, different disinfection methods vary in their effectiveness in combating different types of water contaminants. If you rely on a single disinfection method, for example chlorine disinfection, your water supply could still be contaminated by cryptosporidium, or if chemical contaminants are present, those, too, might remain. Details are at WATER DISINFECTION LIMITATIONS.


Continue reading at WATER DISINFECTION LIMITATIONS or select a topic from the More Reading links shown below.



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