Hardness of the water is defined as the, soap destroying capacity of the water. If the hardness of the water is high then the soap destroying capacity of the water will be less. Other way it can expressed as amount of dissolved calcium and magnesium bicarbonates and sulphates in the water. Hard water always contains higher amount of bicarnoates and sulphates as compared to soft water.
Hard water contains minerals like calcium, magnesium, phosphates in a greater amount which are beneficial for the teeth. Soft water lacks such essential minerals for the tooth protection. Hence, it can be fairly recommended to use hard water only for rinsing the mouth after tooth brushing as, it may help in mineralization process. Long term systemic consumption of hard water, does not pose promising health benefits .For this purpose, systemic consumption of soft water is advised. But, enough literature evidence is required to prove the definite benefits of hard water over dental health.