A measure of the acid-neutralizing capacity (ANC) of water. Acid-neutralizing capacity means the ability to accept acid without a subsequent drop in pH. The more acid that can be added to water before the pH starts to drop, the higher the alkalinity.

Alkalinity is a measure of the buffering ability of water. It is not the measurement of just one substance or ion. It is the combined property of many anions (negative charged ions). To a great extent, the alkalinity of most waters is determined by the amount of bicarbonate and carbonate present in the water. But other substances such as hydroxide, phosphates, silicates and borates also contribute to the alkalinity.