Question

what do you understand by hard water and soft water ?
how many types of hardness in water?

Answer 1

Key Difference: Hard water is water that has a high mineral content, commonly magnesium and calcium. Soft water is water that has a higher sodium content and small concentration of calcium and magnesium.

Answer 2

Hard water =
Water that produces curd with soap and produces very little lather
is called hard water. Hard water affects cleaning ability of soap."
Hard water contains bicarbonate, chlorides and sulphates ( any one or all ) of calcium and magnesium .

soft water =
Water that produces lather with soap easily is called soft water.
Soft water does not affect cleaning action of soap"