Few things are more important to your health and survival during a long emergency than having water that is safe to drink. Knowing how to purify water can help you if your regular water supply becomes contaminated or if you are in a place where clean water is not available. Even if you have stored clean water to use in an emergency, you may run out before the emergency situation has ended.

Water purification can greatly reduce your chance of getting sick from bacteria, viruses, and other living organisms in the water. You can disinfect water using one of the following methods:

• Bring the water to a rolling boil for 1 minute. If you are at an elevation of 6562 ft (2000 m) or higher, boil the water for 3 minutes. This is the most effective purification method but may be impractical if you need large quantities of water. It also requires a heat source, which may not be available in some emergency situations. If fuel or power for your heat source is limited, bringing the water to a boil will usually disinfect it, even if you cannot boil it for the recommended time.
• Add 16 drops of household liquid bleach per gallon of water, stir, and let it stand for 30 minutes. If the water does not smell slightly like bleach after 30 minutes, add 16 more drops of bleach and let it stand for another 15 minutes. You should notice a bleach smell.
• Use iodine or chlorine purification tablets or drops. These are available at stores that sell camping equipment and at some drugstores. Follow the instructions on the package. Purification tablets are not as effective as boiling or disinfecting with bleach, but they do eliminate some types of organisms.
• Water filters can get rid of some microorganisms and improve the taste of water. There are many different types of filters, so be sure that you know what kinds of organisms your filter is effective for.

None of the purification methods described above eliminates heavy metals, salts, chemicals, or radioactive dust or dirt (fallout) from water. Many of these substances can be removed by distilling water, a more complicated method of purifying water.

Radioactive fallout can also be minimized using a homemade filter:

1. Punch holes in the bottom of a bucket, and cover the bottom with 1.5 in. (3.8 cm) of gravel. Cover the gravel with a towel.
2. Place the bucket over a larger container, and pour the water into the bucket so that it filters through the towel and gravel and drains into the container below.
3. Disinfect the water by boiling, adding chlorine bleach, or using purification tablets as described above.
4. Replace the gravel after every 50 quarts of water.