An expression of the total amount of basic anions (hydroxyl groups) present in a solution. In water analysis, it also represents the presence of carbonate, bicarbonate, and occasionally borate, silicate, and phosphate salts that react to produce hydroxyl groups. Bicarbonate and carbonate ions are expected to be in most waters. Hydroxide may occur in water that has been softened by the lime soda process or has been in contact with fresh concrete. Alkalinity furnishes a guide in choosing appropriate treatment of either raw water or plant effluents.