Limescale

Limescale is the hard, off-white, chalky deposit found in kettles, hot-water boilers and the inside of inadequately maintained hot-water central heating systems. It is also often found as a similar deposit on the inner surface of old pipes and other surfaces where "hard water" has evaporated.

Other than being unsightly and harder to clean, limescale can impair the operation of various components or damage them.

In kettles, limescale acts as an insulator, impairing heat transfer. Additionally, it can damage the heating element, which overheats due to accruing limescale.