How to Boil or Treat Contaminated Drinking Water

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5 ways to get clean, safe drinking water

Co-authored by Hannah Young and Aimee Payne, MFA

Last Updated: August 8, 2024 Fact Checked

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• Boiling Water to Purify It
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• Sterilizing Water with Chlorine
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• Purifying Water with Iodine
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• Using Water Disinfection Tablets
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• Improving Water Quality with Light
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• Tips

|Show more |Show less

When you don’t have access to clean tap water, knowing how to boil water is a necessity. Whether you’re camping or your local government has issued a notice directing you to boil water, proper sterilization makes your water safe to drink by killing bacteria and other microscopic organisms. Read on to learn 5 ways to disinfect water to ensure you and your family have safe drinking water in an emergency.

How to Disinfect Drinking Water by Boiling

Pour the water into a pot and place it on a heat source. Wait for the water to come to a rolling boil, then allow it to boil for 1-3 minutes to disinfect it and make it safe to drink. Let the water cool for 30 minutes before drinking.

Steps

Method 1

Method 1 of 5:

Boiling Water to Purify It

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1. 
   1
   Filter the water before boiling it if it is cloudy. Cloudy water is caused by dirt and other debris you don’t want to drink. Let the water rest until the sediment settles to the bottom of the container. Then, secure a clean cloth over an empty container’s opening with a rubber band. Pour the water through the cloth into the covered container. When you've poured all the water through, remove the cloth carefully to avoid dumping the sediment back into the water.

   • Use a paper towel or coffee filter if you don’t have a clean cloth available.
2. 
   2
   Bring the water to a boil over high heat on a stove. Pour the water into a pot safe for use on a stovetop. Then, turn up the heat and wait until the water begins to bubble ferociously. Bubbles should rapidly rise from the bottom of the pot without pause.

   • If you’re familiar with cooking techniques, this is called a rolling boil. Don’t start your timer until the water bubbles consistently.
   • The water can take a while to boil, especially if you’re heating large quantities. Expect it to take at least 5 or 10 minutes and reach a temperature of at least 212 °F (100 °C).
   • Speed up the process by starting with hot water if possible and only boiling as much water as you need. Using a tea kettle or a wide shallow pot with a lid also helps water boil faster.
   • If your stove isn’t operational, use another heat source, such as a campfire or portable stove.
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3. 
   3
   Boil the water for 1-3 minutes, depending on your altitude. If you are in an area 5,000 ft (1.5 km) or more above sea level, water boils at a lower temperature. To make sure your water is clean, boil it for a full 3 minutes. At altitudes lower than this, boil the water for at least 1 full minute. Boil it longer if you’re not sure about the altitude in your area.

   • Read a topographical map to find elevation information. Maps are available online or at your local government’s land survey office.
4. 
   4
   Cool the water for 30 minutes before using it. Hot water takes a while to cool, so plan on boiling it before you need it. Test the water with a kitchen thermometer to make sure it won’t scald you, or hold your fingers close to the water to see if you feel any residual heat.
5. 
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   Improve the water’s taste by adding salt to it. Boiled water often tastes flat – similar to old soda – due to the loss of air. Improve it by mixing in about 1 teaspoon (7 g) of salt per ¹⁄₄ US gal (0.95 L) of water. Stir the salt thoroughly in the water and add more if the taste still isn’t desirable.

   • Another way to improve the water is to aerate it again. Get another clean container and pour the water back and forth between the two containers a few times.
6. 
   6
   Store excess water in a clean, covered container. In case of emergencies, store any water you boil in a resealable container. You don’t need plastic water bottles. Mason jars, plastic jugs, and other resealable containers work well. Keep the container sealed to avoid contamination.

   • Boil and store water in advance! Then you will have a water supply no matter what circumstances you face.
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Method 2

Method 2 of 5:

Sterilizing Water with Chlorine

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1. 
   1
   Disinfect water with chlorine bleach if you can’t boil it. Read the label on regular, unscented liquid bleach to find out how much sodium hypochlorite is in the mixture. For bleach consisting of 6% sodium hypochlorite, add 8 drops from a sterilized eye dropper per 1 US gal (3.8 L). For bleach consisting of 8.25% sodium hypochlorite, reduce the number of drops to 6 per 1 US gal (3.8 L).

   • Water purified with bleach has a slight chlorine smell before it’s safe to drink. If it doesn’t, repeat the treatment.
   • If the chlorine taste is too strong, pour the water into another container to aerate it, then let it rest for a few hours.
2. 
   2
   Mix granular calcium hypochlorite into the water for a stronger purifier. Mix about 1 teaspoon (7 g) of calcium hypochlorite (or powdered swimming pool chlorine) into 2 US gal (7.6 L) of water until it dissolves. Then, stir about ¹⁄₂ US gal (1.9 L) of the mixture into 12.5 US gal (47 L) of water. If the water tastes too strongly of chlorine, pour it into another container and let it stand for a few hours.

   • Granular calcium hypochlorite is very strong, so wear eye goggles and work in a well-ventilated area!
   • Granular calcium hypochlorite is used in pools, so it’s available wherever pool supplies are sold.
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Method 3

Method 3 of 5:

Purifying Water with Iodine

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1. 
   1
   Use household iodine if you don’t have chlorine available. Use a sterilized eye dropper to add about 5 drops of iodine to each ¹⁄₂ US gal (1.9 L) of water. Add 5 extra drops if the water is cloudy. Stir the water thoroughly, then leave it alone for at least 30 minutes before drinking it.

   • Most general stores stock iodine in the pharmacy section. Look for products labeled household iodine or tincture of iodine.
   • Iodine may be included in commercial first-aid kits. Consider keeping a bottle on hand if your kit doesn’t have one already.

Method 4

Method 4 of 5:

Using Water Disinfection Tablets

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1. 
   1
   Purchase water disinfection tablets for an easier way to clean water. Water disinfection tablets are by far the easiest purifier to use. Simply drop 2 tablets into 1 quart (0.95 L) of water and let it dissolve. These tablets come in a variety of strengths, so read the manufacturer’s instructions for safe handling information.

   • Tablets are also available at many pharmacies and sporting goods stores.
   • Chlorine, iodine, and various other types of disinfection tablets are available. Using them means you don’t have to measure out any liquid chemicals.
   • If you don’t like the taste of water purified with these chemicals, try adding other flavors.
   • Registered Dietitian and Trained Chef Jennifer Lease recommends adding fresh fruit, herbs, or a little fresh citrus juice, like lemon, lime, or orange.
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Method 5

Method 5 of 5:

Improving Water Quality with Light

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1. 1
   Use a portable ultraviolet light (UV) to clean small amounts of water. A measured dose of UV light kills some germs in small amounts of clear water. However, it doesn’t work as well if the water is cloudy because the small particles of silt may stop the light from reaching the germs. Also, the portable UV water purifier must have sufficient battery power or it may not safely disinfect the water.

   • Filter the water if it isn’t clear by pouring it through a clean cloth or paper towel.
   • Turn the UV purifier on and check that the battery is full, then place the purifying wand in the water.
   • Leave the purifier in the water for at least 90 seconds. (Refer to the instructions for your purifier for more information and exact timings.)
   • This method is not as effective as boiling or using a chemical disinfectant. However, adding a small amount of iodine or chlorine may help improve and maintain water quality.
2. 2
   Place a clear plastic bottle full of water in the sun to purify it. In an emergency, it’s possible to improve the quality of your drinking water by using solar disinfection. Clean a clear plastic water bottle and fill it with clear water. This type of disinfection isn’t effective on cloudy water. Lay the bottle down on its side in the sun and leave it for 6 hours. If it’s cloudy outside, leave the bottle for 2 days before drinking it.

   • Place the bottle on a dark surface to help the sun more effectively disinfect your water.
   • This method may reduce some germs in your water, but it’s not recommended if other, more effective methods are available.
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Tips

• Boiling water is useful if you get caught in a natural disaster or have to deal with a broken pipe in your area.
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• Listen to your local government when they issue boil advisories. These warnings are for your own safety. Avoid drinking tap water if you aren’t sure it is safe.
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• If you collect water from outside of your home, avoid water that is stagnant or has debris floating in it. Also, avoid water that looks dark or smells bad.
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