what is that stuff that collects on your sink?

What is that weird white chalky looking stuff that collects on your bathroom sink? I think it comes from the use of toothpaste but I am not sure. Does anybody know what causes it and does anybody know how to prevent it from happening or how to get rid of it? It really bothers me. Any help would help much. Thanks:confused:

It’s probably calcium and other minerals in your water. Do you also have this on the tap where the water comes out? What about on your shower head?

It is grahdoo. (Pronounced grah-DOO) Surely you know what grahdoo is?