Surprisingly, water underground is about 60 times as plentiful as fresh water in lakes and rivers on the land surface (not including water stored as ice in glaciers). Groundwater is a tremendously important resource. How it gets underground, where it is stored, how it moves while underground, how we look for it, and, perhaps most important of all, why we need to protect it are the main topics of this chapter.
Also important is how groundwater is related to surface rivers and springs. Groundwater can form distinctive geologic features, such as caves, sinkholes, and petrified wood. It also can appear as hot springs and geysers. Hot groundwater can be used to generate power.
