Water that contains a great number of positive ions. The hardness is determined by the number of calcium and magnesium atoms present. Soap usually dissolves badly in hard water. While hard water in itself is considered a health concern, it is a nuisance due to its likelihood of producing the buildup of minerals in pipelines and heating devices, including in household appliances such as detergent or soap. The mineral buildup creates performance issues by not allowing these equipment to function as well. The most common minerals found in water that produce hardness when dissolved are magnesium and calcium.