Which type of hardness does not include carbonate ions?

Noncarbonate hardness refers specifically to the portion of water hardness that is attributable to species other than carbonate ions, such as sulfates and chlorides of calcium and magnesium. In water chemistry, total hardness encompasses both carbonate and noncarbonate hardness. Carbonate hardness is specifically associated with the presence of carbonate ions and bicarbonate ions in water, contributing to the buffering capacity and precipitation of calcium carbonate.

When evaluating the types of hardness, noncarbonate hardness is important for understanding the treatment and management of water, especially in contexts where carbonate scaling or buffering is not a factor. Identifying the distinctions between these types of hardness is crucial, as it affects decisions related to water treatment processes and the maintenance of plumbing systems. Thus, noncarbonate hardness is correctly identified as the type of hardness that does not include carbonate ions.