If you take a walk in some of the most beautiful landscapes in the UK you often find that that landscape has been caused by limestone being dissolved by the rain. This is a completely natural occurrence and gives us great varity above and below ground!
The reason it dissolves the rock is because the rain has a lot of carbon dioxide in it, which makes the rain mildly acidic.
Below ground, cave stalactites etc
Most caves are made from soluble rocks being very slowly dissolved by the rain moving through them. This also creates the fantastically beautiful stalactites and stalagmites, and choosing a photo to illustrate this is very hard indeed!
So this limescale comes from dissolved rock! Limestone pavements and caves are caused by rain water slowly dissolving the rock. This suspended rock will often stop being suspended in your home, and can cause a tremendous amount of damage to your plumbing system.