Acid Demand

by Pure Water Annie


Acid demand can be defined as the amount of acid needed to reduce the pH level of water.  Acid demand is frequently measured in swimming pool applications by a test known as an acid demand test.

Results of the test are applied to a specific amount of water to determine what amount of acid to add to the water to achieve the desired pH.

Acid demand is strongly affected by the alkalinity of the water, which is a measure of the water’s resistance to pH change. The higher the alkalinity, the more acid that will be needed to lower the pH.

Acid demand tests used by pool owners are usually titration tests, where a reagent is added to the test solution and the drops counted to determine the “acid demand.”

Acids that are commonly used for lowering pH in residential water treatment are citric acid, muriatic acid, and vinegar.  Muriatic acid and sodium bisulfate are commonly used to reduce pH and alkalinity in swimming pools.