How Does An Aquifer Work To Clean And Store Fresh Drinking Water?

When the water goes through the ground it has to go through a lot of sediments after the sediments then are the rocks, the rocks have pores which the water will pass through to get in to the aquifer. By the time the water reaches the aquifer the water should be pretty clean.
  - ProSniper
  P.S-(Sorry It Only Answers Part Of The Question) X__X

Asking is work,,,Duh!