Access to adequate supplies of fresh water is becoming an increasingly critical issue in many parts of the world. In arid regions of the southwestern United States, diminishing water supplies and extended periods of drought have generated an interest in non-traditional water resources, and the development of new technologies such as desalination of brackish water to exploit those resources. New Mexico has limited supplies of fresh water, but over the last century there have been claims that the state has very large reserves of brackish groundwater (e.g., Hood and Kister, 1962; McLean, 1970). However, our knowledge of the quality and volume of these brackish water resources varies significantly across the state. Some aquifers and groundwater basins in more densely populated areas have been very thoroughly investigated by multiple individuals and agencies over time periods of years or decades. Despite this foundation of pre-existing research, our knowledge of the distribution of brackish groundwater in many aquifers in New Mexico is often poorly constrained.