Bicarbonate alkalinity (HCO3-) is one of the three principle forms of alkalinity present in many surface waters and may be classified stoichiometrically by comparing the values for total (T) and phenolphthalein (P) alkalinity. Bicarbonate alkalinity is present when the phenolphthalein alkalinity is less than one-half the total alkalinity and is equal to the total alkalinity less twice the phenolphthalein alkalinity (T-2P). The results are typically expressed in milligrams per liter of equivalent calcium carbonate.
