If it does not, add the same amount of bleach again and let the water stand for 15 more minutes. Due to recent publicity, some people may be concerned about potentially harmful effects of chlorine in drinking water. They're available at camping and sporting goods stores, military surplus stores, and some large department or drug stores. Carefully follow directions on the package. Purification tablets are for emergency use only, not everyday use.
Unopened tablets have a shelf life of several years.
Some tablet kits have additives to help the off-taste and color caused by iodine. In an emergency, iodine in a medicine kit will purify water. Using a medicine dropper, add 20 drops per gallon to clear water and 40 drops per gallon to cloudy water. Mix completely by stirring or shaking in a clean container. Allow the water to stand at least 30 minutes before using.