What is hard and soft water?

Hard water: A sample of water which does not produce lather with soap readily is called hard water. The hardness of water is due to the presence of bicarbonates, chlorides and sulphates of calcium and magnesium dissolved in water, e.g. sea water, river water, lake water and well water.
Soft water. A sample of water which produces lather with soap readily is called soft water. This type of water either does not contain or contains negligible amounts of dissolved salts in it. For example, rain water distilled water and demineralised water.