Groundwater is water found underground, with different definitions depending on the field. Agronomists see it as any water below ground, engineers call it subsurface water, and hydrogeologists define it as water in the saturated zone. Groundwater can be found in rocks like aquifers that hold and transmit water, aquicludes that don't transmit water well, and aquitards that hold water but don't transmit it efficiently. It exists in fractures or open spaces in rocks.