Hydrology and groundwater expert witnesses can tell you that about ¼ of the water used for personal, commercial/industrial, and irrigation uses in the U.S. comes from groundwater. With increasing demands placed on surface water resources, it is likely the demand for groundwater will increase.
In some places, this resource has already been severely tapped, and even mismanaged. An example is the surface water decline in the Republican River watershed of Nebraska and Kansas where over-pumping of groundwater for irrigation in Nebraska has depleted surface water available for downstream flow and use in Kansas resulting in a lawsuit. The State of Kansas filed a complaint to the U.S. Supreme Court that claimed the State of Nebraska had violated the Republican River Compact by allowing the unimpeded development of thousands of wells in hydraulic connection with the Republican River and its tributaries. Kansas further alleged that Nebraska was using more water than its allocation.