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Making Water Safe in an Emergency

In an emergency, water contaminated with germs can often can be made safe to drink by boiling, adding disinfectants, or filtering.

IMPORTANT: Water contaminated with fuel or toxic chemicals will not be made safe by boiling or disinfection. Use bottled water or a different source of water if you know or suspect that your water might be contaminated with fuel or toxic chemicals.

If your water is contaminated during an emergency, use bottled water if possible; bottled water is the safest choice for drinking and all other uses. If bottled water is not available, the following methods can help make your water safe to drink.  

*Note: These methods are listed in order of what is most effective at making your water safe.

1. Boiling

If you don’t have safe bottled water, you should boil your water to make it safe to drink. Boiling is the surest method to kill disease-causing organisms, including viruses, bacteria, and parasites.

You can improve the flat taste of boiled water by pouring it from one container to another and then allowing it to stand for a few hours, OR by adding a pinch of salt for each quart or liter of boiled water.

If the water is cloudy:

  1. Filter it through a clean cloth, paper towel, or coffee filter OR allow it to settle.
  2. Draw off the clear water.
  3. Bring the clear water to a rolling boil for 1 minute (at elevations above 6,500 feet, boil for three minutes).
  4. Let the boiled water cool.
  5. Store the boiled water in clean sanitized containers with tight covers.

If the water is clear:

  1. Bring the clear water to a rolling boil for 1 minute (at elevations above 6,500 feet, boil for three minutes).
  2. Let the boiled water cool.
  3. Store the boiled water in clean sanitized containers with tight covers.

2. Disinfectants

If you don’t have safe bottled water and if boiling is not possible, you often can make small quantities of filtered and settled water safer to drink by using a chemical disinfectant such as unscented household chlorine bleach. Disinfectants can kill most harmful or disease-causing viruses and bacteria, but are not as effective in controlling more resistant organisms, such as the parasites Cryptosporidium and Giardia. Chlorine dioxide tablets can be effective against Cryptosporidium if the manufacturer’s instructions are followed correctly. If the water is contaminated with a chemical, adding a disinfectant will not make it drinkable.

To disinfect water with unscented household liquid chlorine bleach:

If the water is cloudy:

  1. Filter it through a clean cloth, paper towel, or coffee filter OR allow it to settle.
  2. Draw off the clear water.
  3. Follow the instructions for disinfecting drinking water that are written on the label of the bleach.
  4. If the necessary instructions are not given, check the “Active Ingredient” part of the label to find the sodium hypochlorite percentage, and use the information in the following table as a guide. Typically, unscented household liquid chlorine bleach will be between 6% and 8.25% sodium hypochlorite, though concentrations can be different. Using the table below, add the appropriate amount of bleach using a medicine dropper, teaspoon, or metric measure (milliliters).
  5. Stir the mixture well.
  6. Let it stand for at least 30 minutes before you use it.
  7. Store the disinfected water in clean, sanitized containers with tight covers.

If the water is clear:

  1. Follow the instructions for disinfecting drinking water that are written on the label of the bleach.
  2. If the necessary instructions are not given, check the “Active Ingredient” part of the label to find the sodium hypochlorite percentage, and use the information in the following table as a guide. Typically, unscented household liquid chlorine bleach will be between 6% and 8.25% sodium hypochlorite, though concentrations can be different. Using the table below, add the appropriate amount of bleach using a medicine dropper, teaspoon, or metric measure (milliliters).
  3. Stir the mixture well.
  4. Let it stand for at least 30 minutes before you use it.
  5. Store the disinfected water in clean, sanitized containers with tight covers.

 

Making water safe to use with bleach having a 1% concentration of sodium hypochlorite
* If the water is cloudy, murky, colored, or very cold, add double the amount of bleach listed below
1 quart/liter water 1 gallon water 5 gallons water
If you have a dropper:
Add 10 drops of bleach
If you have a dropper:
Add 40 drops of bleach
If you have a dropper:
Add 200 drops of bleach
If you have something that measures milliliters (ml):
Add ½ ml of bleach
If you have something that measures milliliters (ml):
Add 2½ ml of bleach
If you have something that measures milliliters (ml):
Add 12½ ml of bleach
If you have a measuring spoon:
Add ⅛ teaspoon of bleach
If you have a measuring spoon:
Add ½ teaspoon of bleach
If you have a measuring spoon:
Add 2½ teaspoons of bleach

 

Making water safe to use with bleach having a 6% concentration of sodium hypochlorite
* If the water is cloudy, murky, colored, or very cold, add double the amount of bleach listed below
1 quart/liter water 1 gallon water 5 gallons water
If you have a dropper:
Add 2 drops of bleach
If you have a dropper:
Add 8 drops of bleach
If you have a dropper:
Add 40 drops of bleach
If you have something that measures milliliters (ml):
Add 0.1 ml of bleach
If you have something that measures milliliters (ml):
Add ½ ml of bleach
If you have something that measures milliliters (ml):
Add 2½ ml of bleach
If you have a measuring spoon:
Amount too small to measure
If you have a measuring spoon:
Add a little less than 1/8 teaspoon
If you have a measuring spoon:
Add ½ teaspoon of bleach

 

Making water safe to use with bleach having an 8.25% concentration of sodium hypochlorite**
* If the water is cloudy, murky, colored, or very cold, add double the amount of bleach listed below
1 quart/liter water 1 gallon water 5 gallons water
If you have a dropper:
Add 2 drops of bleach
If you have a dropper:
Add 6 drops of bleach
If you have a dropper:
Add 30 drops of bleach
If you have something that measures milliliters (ml):
Amount too small to measure
If you have something that measures milliliters (ml):
Add ½ ml of bleach
If you have something that measures milliliters (ml):
Add 2 ml of bleach
If you have a measuring spoon:
Amount too small to measure
If you have a measuring spoon:
Add a little less than 1/8 teaspoon
If you have a measuring spoon:
Add ⅓ teaspoons of bleach

**8.25% is the most common household bleach concentration available

 

Making water safe to use with bleach having an unknown concentration of sodium hypochlorite
* If the water is cloudy, murky, colored, or very cold, add double the amount of bleach listed below
1 quart/liter water 1 gallon water 5 gallons water
If you have a dropper:
Add 10 drops of bleach
If you have a dropper:
Add 40 drops of bleach
If you have a dropper:
Add 200 drops of bleach
If you have something that measures milliliters (ml):
Add ½ ml of bleach
If you have something that measures milliliters (ml):
Add 2½ ml of bleach
If you have something that measures milliliters (ml):
Add 12½ ml of bleach
If you have a measuring spoon:
Add ⅛ teaspoon of bleach
If you have a measuring spoon:
Add ½ teaspoon of bleach
If you have a measuring spoon:
Add 2½ teaspoons of bleach

To disinfect water with tablets that contain chlorine or iodine:

  • Follow the manufacturer’s instructions on the label or in the package.
    • Chlorine dioxide tablets can be effective against Cryptosporidium if the manufacturer’s instructions are followed correctly.
    • Iodine and iodine-containing tablets (tetraglycine hydroperiodide) or chlorine tablets are not effective against Cryptosporidium.

3. Filters

Many portable water filters can remove disease-causing parasites such as Cryptosporidium and Giardia from drinking water. If you are choosing a portable water filter, try to pick one that has a filter pore size small enough to remove parasites. Most portable water filters do not remove bacteria or viruses.

Carefully read and follow the manufacturer’s instructions for the water filter you intend to use. After filtering, add a disinfectant such as iodine, chlorine, or chlorine dioxide to the filtered water to kill any viruses and remaining bacteria.

For more information about water filters that can remove parasites, see the CDC’s A Guide to Water Filters.

4. Distillation

You may also be able to make water safe by distilling it or by boiling water and collecting the steam in a clean container so it turns back into water.

Learn more about distilling water:

Other Methods

To learn more about other methods of water treatment  visit CDC’s Traveler’s Health Water Disinfection page.

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