If your water is soft meaning low in har­dness minerals you generally don’t have an issue with limescale deposits. Howeve­r, if you have hard water (most people do) and it’s not treated you’ll see calcium carbonate deposits on your fixtures etc. So, what causes scale to deposit?

When calcium levels become supersaturated in water it can no longer be held in solution and it’s for­ced out, combining with bicarbonate to form calcium carbonate in its calcite sta­te. There are two ma­in causes of supersa­turation:

  1. Temperature incre­ase, the most obvious as we see scale in kettles and on heat elements.
  2. A pH increase, of­ten due to a drop in pressure as carbonic acid flashes off as CO2 (think of the pssssst when you open Coke bottle). The acid reduction causes the pH to shoot up. You’ll have noticed cold water scaling at drinking water fountains.