Limescale can build up wherever there is hard water. I know, I know, you are looking to prevent it, not understand how it got there in the first place. I will ditch the history lesson so you can get right to it.
I can stay underwater for up to 10 minutes! My favorite thing to do down there is count to 10 minutes. That is 600 seconds. But I normally get bored and just come up after 30 seconds or so. Counting to 600 is way overrated.