The hydrologic cycle -- The Earth's water transfer system is called the hydrologic cycle. The water system is powered by the sun. 97.2% of the Earth's total water is in the oceans. 2.2% is in ice caps and glaciers. 0.6% is in groundwater, rivers, lakes and the atmosphere.

Freshwater budget -- Groundwater is 14% of freshwater in hydrosphere. The average rate of groundwater exchange is 280 years. Exchange means the transfer from the atmosphere to the ground and back to the atmosphere. This exchange rate gives an indication that groundwater movement is slow.

Water table -- The water table defines the top of the zone of saturation, where groundwater occurs. Porosity governs the amount of groundwater that a rock material can hold. The water table is not flat. The water table is higher under hills than under valleys. Groundwater flow is impeded by indirect flow around grains.

Permeability -- Permeability defines the ability of a porous rock to transmit a fluid. Permeable layers are called aquifers. Impermeable layers are called aquicludes. Springs arise from a perched water table. Otherwise groundwater discharges into streams as a consequence of flowing from a higher water under hills towards the lower water table in valleys. If water discharges into a stream, the water table comes to surface right at the stream. In this case the water table slopes downhill toward the stream.

Mining Groundwater -- Wells are drilled into the zone of saturation below the water table. When wells are pumped, the water flows to the well which locally depresses the water table (drawdown) and creates a cone of depression.

Groundwater is an exhaustible resource.