The two main elements that are found in hard water are calcium and magnesium. Other elements are found in hard water as well, including iron, manganese and aluminum.
The term hard water typically correlates with the water's ability to lather soap. Hard water typically makes less lather, and soft water will have more. In natural water, limestone is the main cause of water hardness. Areas that are rich in granite will have softer water. The hardness or softness of water can be important to nearby industries. For example, beer brewing requires water with 200 to 300 mg/L of hardness, while water for washing clothes should have hardness of 50 mg/L or less in order to be effective.