A.N.T.S

Water 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 a different source of water if you know or suspect that water might be contaminated with fuel or toxic chemicals.

Boiling

If you don’t have safe bottled water, you should boil water to make it safe. Boiling is the surest method to make water safer to drink by killing 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,

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

If the water is clear,

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

If you don’t have clean, safe, bottled water and if boiling is not possible, you often can make water safer to drink by using a disinfectant, such as unscented household chlorine bleach, iodine, or chlorine dioxide tablets. These can kill most harmful organisms, such as viruses and bacteria. However, only chlorine dioxide tablets are effective in controlling more resistant organisms, such as the parasite Cryptosporidium.

To disinfect water,

• Clean and disinfect water containers properly before each use. Use containers that are approved for water storage. Do not use containers previously used to store chemicals or other hazardous materials.
• Filter it through a clean cloth, paper towel, or coffee filter OR allow it to settle.
• Draw off the clear water.
  • When using household chlorine bleach:
    • Add 1/8 teaspoon (or 8 drops; about 0.625 milliliters) of unscented liquid household chlorine (5–6%) bleach for each gallon of clear water (or 2 drops of bleach for each liter or each quart of clear water). Add 1/4 teaspoon (or 16 drops; about 1.50 milliliters) of bleach for each gallon of cloudy water (or 4 drops of bleach for each liter or each quart of cloudy water).
    • Stir the mixture well.
    • Let it stand for 30 minutes or longer before you use it.
    • Store the disinfected water in clean, disinfected containers with tight covers.
  • When using iodine:
    • Follow the manufacturer’s instructions.
    • Store the disinfected water in clean, disinfected containers with tight covers.
  • When using chlorine dioxide tablets:
    • Follow the manufacturer’s instructions.
    • Store the disinfected water in clean, disinfected containers with tight covers.

Many portable water filters can remove disease-causing parasites such as Cryptosporidium and Giadia 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 both bacteria and parasites. Most portable water filters do not remove viruses.

Carefully read and follow the manufacturer’s instructions for the water filter you intent 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. 

To learn more about water filters and treatments that can remove microorganisms such as viruses, bacteria, and parasites (such as Cryptosporidium), see the following resources:

A Guide To Water Filters

A Guide To Drinking Water and Sanitation For Backcountry Travel Use

Covers information on the effectiveness of various water treatment methods. 

Drinking Water Treatment Methods for Backcountry and Travel Use - PDF

WATER FILTRATION DEVICES - Army Field Manual

6-35. If the water you find is also muddy, stagnant, and foul-smelling, you can clear the water—

By placing it in a container and letting it stand for 12 hours.

By pouring it through a filtering system.

NOTE: These procedures only clear the water and make it more palatable. You will have to purify it.

To make a filtering system, place several centimeters or layers of filtering material such as sand, crushed rock, charcoal, or cloth in bamboo, a hollow log, or an article of clothing (Figure 6-10).

Figure 6-10. Water Filtering Systems

6-37. Remove the odor from water by adding charcoal from your fire. Charcoal is also helpful in absorbing some agricultural and industrial chemicals. Let the water stand for 45 minutes before drinking it.