Why Hard Water can not Lather Easily with Soap but Soft Water Easily Does
Hard water such as river water, borehole water and sea water have high concentration of dissolved mineral salts such as Iron, Magnesium and Calcium salt (Fe2+, Mg2+ and Ca2+ ions) which react with soap to form scum. Some soft water contains very little or no dissolved minerals.
Some hard water can lather with soap faster than others, even though there will be difficulties. This is based with the mineral concentration level of the water.
The major difference between hard and soft water is their ability to lather with soap. Hard water can be softened in order to make it lather with soap easily.