Hard water is any water that forms a scum with soap. Soft water forms lather with soap.
Hardness is caused by dissolved calcium and magnesium icons (Ca2+ and Mg2+).
Temporary hardness
- Temporary hardness can be removed by boiling the water.
- Problems caused by temporary hardness: forms scum (wastes soap), limescale forms in pipes (blocks the pipe) and kettles (wastes heat).
Permanent Hardness
- Permanent hardness can be removed by icon exchange (deionisation) (this works for temporary hardness too). It cannot be removed by boiling the water.