Hydrogeology is in many ways just what it sounds like: a cross between hydrology and geology. Its main focus is on aquifers or permeable, sponge-like portions of earth under the surface that foster groundwater. Hydrogeology is also variously referred to as geohydrology and saturated subsurface hydrology. It is important for hydrologists to consider where water is located underground, how it flows, and what its fate will be in the hydrological cycle on the whole. This consideration is especially important as the human race seeks additional clean water sources in light of increasing levels of pollution.