pH is the index indicating the degree of alkalinity or acidity. The pH value is expressed by a figure from 0 to 14 indicating the concentration of hydrogen ion (H+) in the water according to the following equation: pH = -log [H+] Values near pH7 are neutral, and as the values become closer to 14 they become more strongly alkaline. On the other hand, as the values become closer to 0 they become more strongly acidic.