What is groundwater?
Groundwater is water held in pores and fractures of soil and rock beneath the surface.
How it works and what the evidence shows
Core idea Some precipitation infiltrates to the saturated zone. Gravity, pressure and permeability control movement through pores; an aquifer transmits usable quantities of water. Evidence and research Wells and springs provide access. The water table and flow vary with geology and season; monitoring wells and chemistry help characterize them.
Uses and limitations
Why it matters Groundwater supports drinking supplies, irrigation and dry-season river flow. Heavy pumping can lower levels, while pollution may persist for long periods. Common misunderstandings Most groundwater is not a river in a cavern; it occupies small spaces like water in a sponge. A clean well does not prove a neighboring aquifer is safe.