The water system is powered by the sun. 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.
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. Permeable layers are called aquifers. Impermeable layers are called aquicludes.