To be prepared for a drinking water emergency, you should store enough drinking water to supply each person 1 gallon a day. This is the amount normally used by one person for drinking, cooking and teeth brushing. Additional water will be used for sanitation purposes but it does not need to be purified.

Before storing the water, add liquid bleach to the container according to the calculator in order to keep it safe for drinking.

Store in a cool place safe from temperature swings (a basement area works great - garage not so much). It is recommended to rotate your stored water every six months. We have used drinking water stored using this method as much as two years later. The water tasted pure and was crystal clear.

Mix 1 part of 5% household bleach and 4 parts clean water by volume to give 5 parts 1% bleach solution. For example, 1 ounce bleach to 4 ounces of water or 1 cup bleach to 4 cups water.

In addition to using bleach to prepare water for storage it is useful to make questionable water safe to drink in an emergency.

Avoid using scented and "color-safe" bleaches. Household bleach has a strength of about 5% chlorine (most labels show it as 5.25%).

Place the water (filtered if necessary) in a clean container, add the amount of bleach according to the calculator. It is important to mix thoroughly and allow to stand for at least 30 minutes before using the water. If the water is cloudy, or very cold, increase the standing time to 60 minutes. For treating small amounts of water, you may find it easier to use a 1% bleach solution.

Note: Chlorine and other chemicals will not kill cysts of the parasite Cryptosporidium ("Crypto"), which may be present in water supplies affected by untreated surface water. Cryptosporidium is an organism that can cause severe illness and even death in persons who have been weakened because of health problems. Boiling is the best water treatment in these situations.

Much of this information was originally sourced from clorox.com.