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search Limescale (scanning electron microscopy micrograph, field
of view 64 x 90 µm)   It is also often found as a similar
deposit on the inner surface of old pipes and other surfaces
where "hard water" has evaporated. In addition to being
unsightly and hard to clean, limescale seriously impairs the
operation or damages various components.[1]  The type found
deposited on the heating elements of water heaters has a main
component of calcium carbonate. Hard water contains calcium (and
often magnesium) bicarbonate or similar ions. Calcium salts,
such as calcium bicarbonate and calcium carbonate are both more
soluble in hot water than cold water.[dubious ] Thus, heating
water does not cause calcium carbonate to precipitate per se.
However, there is an equilibrium between dissolved calcium
bicarbonate and dissolved calcium carbonate:  Ca2+ + 2HCO3 Ca2+
+ CO32− + CO2 + H2O  where the equilibrium is driven by the
carbonate/bicarbonate, not the calcium. Note