The word ‘hard water’ refers to water with a high mineral content. Hard water is formed when water percolates into calcareous, gypsum, or chalk deposits that are mainly composed of carbonates of magnesium or calcium, bicarbonates, and sulphate.
- Calcium and magnesium salts are commonly found in hard water.
- A precipitate is formed when soap molecules react with calcium and magnesium salts.
- This precipitate starts to float on the surface of the water as an off-white layer. Scum is the name for this layer.
- Because of the formation of scum, soaps lose their cleansing ability in hard water.