Water can be classified based on its ability to form lather with soap. We have soft and hard water.
This is water that forms lather easily with soap. NB: Soft water is good for washing since it foams easily with soap. Again, soft water is good for dyeing and taming because it has no salt that would interfere and disrupt the process.
This is water that does not form lather easily with soap. It is due to the presence of Ca2+ and Mg2+. We have a temporary and permanent hardness of the water.