Groundwater is under the Earth's surface filling voids or openings in rocks and sediment (aquifers). In states like Nevada, where precipitation is minimal, groundwater is an important source of water for many uses especially household, municipal, and agricultural use.
Basin and Range Aquifers
Groundwater in Nevada principally occurs within “Basin and Range aquifers”. The aquifers are formed of volcanic rocks, carbonate rocks, or unconsolidated to consolidated basin-fill deposits. The basin-fill deposits form the most productive aquifers and are generally in individual alluvial basins that are drained internally and are separated by low mountains. Practically all precipitation that falls in the Basin and Range Province is returned to the atmosphere by evapotranspiration, either directly from the soil, or from phreatophytic vegetation or lakes that occupy lower portions of the basins and serve as discharge areas for the alluvial aquifers.
USGS Office of Groundwater maintains a web site with much more information about aquifers throughout the U.S.: Aquifer Basics
The USGS Nevada Water Science Center collects and disseminates a large quantity of groundwater data for Nevada. Depth to groundwater measurements are either made on a continuous basis or as an occasional manual measurement. Continuous data are available from the real-time and daily data links and manual measurements are available from the water levels link. Results from aquifer tests are provided through the Aquifer Test link. Many of the USGS Nevada Water Science Center groundwater investigations directly measure evapotranspiration to estimate groundwater discharge. Evapotranspiration data is provided through the evapotranspiration link.