When water goes down through the ground it gets filtered. That's why some of the purest water is found underground.
When water freezes it turns into ice, glaciers are really big groups of ice in places like Antarctica. When they melt, they turn into water which normally goes into the ocean. This can cause rising sea levels.
When there are wholes in the ground water from rain and rivers etc. can go into the ground. That's why when you dig a whole in the beach you can reach water.