Making Water Safe in an Emergency

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 5-6% 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 5-6% 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.

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.

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.

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:

• FEMA/American Red Cross. Food and Water in an Emergency (page 16).[PDF – 16 pages]

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