This map shows the estimated fresh water usage per square mile in the year 2000 for counties in the eight states underlain in part by the High Plains (Ogallala) Aquifer, presented as million gallons per square mile and million liters per square kilometer.
Usage is for all purposes -- public supply, industrial, irrigation, mining, livestock, and thermoelectric power -- from all underground sources, not just from the Ogallala Aquifer.
Water usage data for the year 2000 was taken from the datafile wu2000t.dbf[1] from the US National Atlas[2].  Citation information from the metadata for that file:

Originator
U.S. Geological Survey, Water Resources of the United States
Publication_Date
200509
Title
Estimated Use of Water in the United States, 2000
Geospatial_Data_Presentation_Form
Database
Publication_Information

Publication_Place
Reston, VA
Publisher
National Atlas of the United StatesOnline_Linkage
&lt;http://nationalatlas.gov/atlasftp.html?openChapters=chpwater#chpwater&gt;Additionally:

Supplemental_Information
Data were drawn from Circular 1268 which serves as one of the few sources of information about regional or national trends in water withdrawals.  Circular 1268 provides information on eight categories of water use: public supply, domestic, irrigation, livestock, aquaculture, industrial, mining, and thermoelectric power.  The complete report can be found at http://water.usgs.gov/pubs/circ/2004/circ1268/The attribute used in this map is described:

Attribute_Label
To-wgwfr
Attribute_Definition
The estimated total ground water withdrawals of fresh water for all categories, in millions of gallons per day.  Totals may include null values (unknowns) for domestic, livestock, or mining use.  These categories generally represent negligible amounts of water use for a county.
Attribute_Definition_Source
National Atlas of the United StatesThe data is supplied as million gallons per day, by county.  To arrive at an annual amount per square mile per year, the usage value from wu2000t.dbf was multiplied by 365 and divided by the number of square miles in the county as given in the 2000 county shapefile co2000p020 from the National Atlas:

Citation_Information

Originator
National Atlas of the United States
Publication_Date
200506
Title
2000 County Boundaries of the United States
Publication_Information

Publication_Place
Reston, VA
Publisher
National Atlas of the United StatesOnline_Linkage
&lt;http://nationalatlas.gov/atlasftp.html&gt;Aquifer boundaries taken from Fischer and McGuire[3].

The map is presented in a Lambert azimuthal equal-area projection as used in the National Atlas (EPSG:2163[4]), the central meridian and latitude of which align nicely with the aquifer.
Own work
Kbh3rd