Hard water is a perfectly natural phenomenon. It contains a high percentage of minerals which are present as salts in solution. They are mainly Calcium and Magnesium based, and they are essential to plant and animal life. Unfortunately, they also cause problems. The main culprit is Calcium Carbonate which is salt responsible for hardness. It is equally responsible for lime scale, because of its rare property of dissolving in cold water and growing in hot water. Most other salts dissolve in hot water.