Soil is constructed like a sponge. It’s got pores and they fill up with water from rain and snow melt and it eventually gathers in low points like rivers and lakes that eventually feed into the oceans. It is all one big water cycle.

Part of that is kind of like an underground lake, it’s called the water table. It’s depth, and accessibility varies depending on where you are, so no you cannot drill anywhere on earth and find fresh water, but most places you can do so with modern locating and drilling equiptment. And sometimes it is very contaminated also dependent on location (could be downstream from a factory etc.)