Hard water contains a lot of calcium and magnesium salts. These ions are good for your health but prevent soap lathering quickly and forms scum.
Soft water has little calcium and magnesium salts and lathers easily.
Types of hardness:
Permanent hardness - caused by calcium sulphate
Temporary hardness - caused by calcium hydrogen carbonate
Rainwater is naturally acidic as it contains dissolved CO2. The south has limestone which is calcium carbonate. The acid in the rain attacks the limestone so it dissolves in the water.
Calcium carbonate + water + carbon dioxide --> Calcium hydrogen carbonate
CaCO3 + H2O + CO2 --> Ca(HCO3)2
Citric acid + Calcium carbonate --> Calcium citrate + carbon dioxide +…