O2 is a liquid concentrate, taken by mixing a number of drops with drinking water. If you use ordinary tap water, the O2 will act to purify the water thus the benefit you receive from the solution is reduced. Boiled water should not be used. O2 has a slightly sour lemon taste; if you find this unpleasant you can then use more water or take O2 diluted with your favorite fruit juice. Some people prefer taking O2 by placing a few drops on the palm of their hand and licking it. The strong taste rapidly changes and neutralizes.