The capacity of water to accept protons is called alkalinity. Alkalinity important in water treatment and in the chemistry and biology of natural waters. Alkalinity serves as a pH buffer and reservoir for inorganic carbon. It helps to determine the abiuty of water to support algal growth and other aqualic life thus, it can be used as a measure of water fertility. n natural waters, the species responsible for alkalinity are OH HCo, and cos before(co, is Alkalinity is equal to[oH] [Hco, +20co, 1.The coeffcient of.2" necessary because carbonate accepts two protons. However, in natural waters of pH 7.9 the predominant species is bicarbonate.