Hard water is water contaminated with compounds of calcium and magnesium. Dissolved iron, manganese, and strontium compounds can also contribute to the "total hardness" of the water, which i [..]

A measure of the amount of metallic salts found in water. Hard water can inhibit the action of some surfactants and reduce the effectiveness of the cleaning process. Weight per Gallon

Soluble metal salts, (principally those of calcium and magnesium, and sometimes iron and manganese) that when present in water in sufficient amounts create cleaning problems. These metal salts remain [..]

A measure of the amount of minerals in water. Mineral compounds that contribute to water hardness are listed in a link in the Learning Library. See also temporary hardness and permanent hardness.

Water containing dissolved calcium and magnesium salts. Temporary hardness results from the presence of bicarbonates and these form a scale when water is heated. Permanent hardness involves sulphates [..]

Hardness, in simplistic terms, is a measure of the mineral content of water, namely the sum of the concentrations of calcium and magnesium cations.