Total hardness is a measurement of the mineral content in a water sample that is irreversible by boiling. Total hardness is determined by the multivalent cations' concentrations present in water. These cations have a positive charge that is higher than 1+. Typically, cations have a charge of 2+. The most common cations present in hard water are Mg2+ and Ca2+. Hardness is caused by calcium and magnesium ions in the water. The presence of bicarbonate ions affects the dose of chemicals required to precipitate the calcium and magnesium, and therefore hardness is classified in two ways: As calcium or magnesium hardness As carbonate or noncarbonate hardness. Carbonate hardness is caused by calcium or magnesium ions associated with bicarbonate ions, and noncarbonate hardness is caused by calcium or magnesium ions associated with chloride, sulfate, or other ions. Total Hardness Hardness also relates to the scale that precipitates in kettles and utensils when water is boiled. The form of hardness produced on heating is the temporary, or carbonate, hardness consisting of calcium and magnesium bicarbonates. Permanent, or non-carbonate, hardness (which is not precipitated by heating) is due to other minerals or salts of calcium and magnesium, such as sulphates, that may be present in the water. Consumers living in hard water areas complained about the scale of deposition on kitchen utensils and increased soap usage, with associated scum formation. Conversely, waters containing less than 30–50 mg/l total hardness tend to be corrosive and may need additional treatment to reduce the risk of plumbo- and cuprosolvency.