Aquifers are large areas of natural underground water-bearing rocks which act like a sponge - chalk and limestone are classic examples.

These natural features below the ground’s surface absorb rainwater that has percolated its way down through the soil over many weeks and months.
 
This water is then stored and gradually flows through the voids, or pore spaces, in the rock, towards springs, rivers or the sea.
 
Water companies drive shafts, called wells or boreholes, down into these aquifers. They lower special pumps into the bottom of these wells or boreholes, and pump water up to the surface where it can be treated to make it safe to drink.