Alkalinity of water is its acid-neutralizing capacity, the sum of all the titratable bases. Because the alkalinity of many surface waters is primarily a function of carbonate, bicarbonate and hydroxide content, it is taken as an indication of the concentration of these constituents. The measured values also may include contributions from borates, phosphates, silicates or other bases if these are present. Alkalinity measurements are used in the interpretation and control of water and waste water treatment processes. Raw domestic waste water has an alkalinity less than, or only slightly greater than that of the water supply.

The content of carbonate is determined by titration of a sample aliquot with a solution of 0.05 N HCl to a pH of 8.3. The bicarbonate concentration is determined by continued titration of the sample aliquot to pH 4.5.

This method is applicable to surface, ground and seawater in the range of 0 mg/L to 5000 mg/L. The range can be increased by increasing the normality of the acid or decreasing the sample volume.