Groundwater

Groundwater = precipitation that does not evaporate, flow into waterways, or get taken up by organisms
Aquifers = Porous sponge-like formations of rock, sand, or gravel that hold groundwater
Zone of aeration = spaces are partially filled with water
Zone of saturation = spaces are completely filled with water
Water table = boundary between the two zones
Aquifer recharge zone = any area where water infiltrates Earth’s surface and reaches aquifers

Confined or artesian = water-bearing, porous rocks are trapped between layers of less permeable substrate (i.e., clay)
Is under a lot of pressure
Unconfined aquifer =  no upper layer to confine it
Readily recharged by surface water
Groundwater becomes surface water through springs or human-drilled wells
Groundwater may be ancient: the average age is 1,400 years