If it does not, add the same amount of bleach again and let the water stand for 15 minutes more. These tablets are iodine based and are specifically made to purify 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 include an additive to help the off-taste and color created 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.