Hydrogeology is a science dealing with the properties,
distribution, and circulation of water on the surface of the
land, in the soil and underlying rocks, and
in the atmosphere. The term "geohydrology" is
sometimes erroneously used as a synonym for
"hydrogeology." Geohydrology is concerned with
underground water. There are many formations that
contain water but are not part of the hydrologic cycle
because of geologic changes that have isolated them
underground. These systems are properly termed
geohydrologic but not hydrogeologic. Only when a
system possesses natural or artificial boundaries that
associate the water within it with the hydrologic cycle
may the entire system properly be termed hydrogeologic.