Treating water

If you are uncertain about the purity of any water source during or after an emergency, you can make it safe to drink by treating it before you use it for drinking, food preparation, or hygiene.

Water sources to avoid altogether

Examples of water sources that should be avoided altogether include:

  • Flood waters
  • Water that has an unusual odor or color (In addition to having a bad odor and taste, water from questionable sources may be contaminated by a variety of microorganisms that can cause dysentery, cholera, typhoid, and hepatitis.)
  • Water that you suspect might be contaminated with fuel, heavy metals, or toxic chemicals. This water cannot be made safe, so you must find a different source of water for your needs.

Ways to make water safe to drink

Most water can be treated by boiling, disinfecting, filtering, purifying, or distilling it. Regardless of the method that you use, make sure that the container(s) you use to treat and store your drinking water in are sanitized. Here are step-by-step instructions for how to do each of these processes:

Boil water for at least one minute

Boiling is the best method to make water safe to drink because it kills disease-causing organisms, including viruses, bacteria, and parasites.

Be sure to strain your water before boiling it if your water is cloudy or has particles in it. You can do this by pouring your water through a clean cloth, paper towel, or coffee filter.

  1. Place water in a clean pot or other container in which you can use to boil water safely.
  2. Bring water to a rolling boil for at least one minute.
  3. Let cool, then use.
  4. Store the boiled water in clean sanitized containers with tight covers for up to a week.

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.

Do not boil water that you suspect might be contaminated with fuel, heavy metals, or toxic chemicals. Boiling this water will actually concentrate the contaminants. Find another source of water.

Disinfect water with household bleach

If you don’t have safe bottled water and if boiling is not practical, you often can make small quantities of water safe to drink by using a chemical disinfectant such as unscented household chlorine bleach. These 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 Giardia and Cryptosporidium.

Here’s how to do it:

  1. Place water in a clean container. (If water is cloudy or has particles in it, be sure to strain it before treating it. You can do this by pouring your water through a clean cloth, paper towel, or coffee filter.)
  2. Add unscented liquid household chlorine bleach* to your water. For clear water, add 1/8 teaspoon (8 drops or about 0.75 milliliters) of bleach for each gallon (16 cups) of water. For cloudy water, add ¼ teaspoon or 16 drops of bleach per gallon.
  3. Mix well and let sit for 30 minutes before using. If you cannot detect a slight chlorine odor after letting it stand for 30 minutes, then repeat the process. If you still do not detect a slight chlorine odor after the second treatment, discard that water and find another source. Bleach potency diminishes with time, so store a bottle with your emergency water supply and replace on the same schedule as your stored water.
  4. Disinfected water can be used for one week if stored in a clean, closed container.

* Sodium hypochlorite (concentration 5.25% to 6%) should be the only active ingredient in the bleach. There should be no added soap or fragrance.

% Sodium HypochloriteDrops per Quart/Liter/Gallon of Clear Water
If the water is cloudy, murky, colored, or very cold, double the amount of bleach added.
1%   10 drops per quart/liter - 40 drops per gallon
4-6%   2 drops per quart/liter - 8 drops per gallon
7-10%   1 drop per quart/liter - 4 drops per gallon
Unknown   10 drops per quart/liter – 40 drops per gallon

Use purification tablets or iodine to treat water

Water purification tablets and iodine, can also be used to treat water. Both can be found at most outdoor stores or through many online vendors. Follow instructions provided on or with the packaging.

Personal water filters

There are many types of personal water filters to choose from, and some of them do a better job of filtering out microorganisms such as viruses, bacteria, and parasites than others. If possible, try to choose a filter with pore size small enough to remove both bacteria and parasites (most don’t remove viruses). Learn more about water filters and treatments that can remove microorganisms such as viruses, bacteria, and parasites (such as Cryptosporidium) here.

Regardless of which filter you choose, be sure to carefully read and follow the manufacturer’s instructions and, if necessary, add disinfectant such as household bleach (see above for instructions) to the filtered water to kill any viruses and remaining bacteria.

Distillation

You may also be able to make water safe by distilling it, or boiling water and then collecting the steam as it condenses back into water. This method will remove microorganisms along with heavy metals, salts, and most other chemicals.

Here’s how to distill water:

  1. Fill a pot halfway with water
  2. Tie a cup to the handle on the pot’s lid so that the cup will hang right-side-up when the lid is upside down (make sure the cup is not dangling into the water)
  3. Boil the water for 20 minutes
  4. The water that drips from the lid into the cup is distilled and safe to drink.