Water purification tablets allow you to chemically treat the water to kill viruses such as Giardia, Cyclosporiasis and others. Tablets are one of the four methods available for purifying water (e.g. filters, UV, chemical, and boiling).
The video below shows you how to properly use these tablets to remove viruses from the water. Its important to note that you need wait the necessary time to let the tablets work properly and kill all the pathogens in the water (read the directions for more information, as the time can vary depending on the type of water treatment you're using).