[The_Damned_One]

What happens is when water is spilled on the ground (in this case it's piss i suppose), heat causes it to evaporate. When water evaporates, it rises, leaving behind everything that is not pure water. When it's in the sky, it forms clouds, and the wind pushes it. Since oceans covers such a vast portion of the surface of the earth, most of these clouds discharge as rain over them, simply putting in pure water. This means there is always the same amount of water on the earth.