A recent article discussed the potential for desalinating brackish groundwater as a potential source of drinking water, specifically in Texas. West Texas is dry and has limited fresh groundwater resources, so it may make economic sense in areas like that.

Brackish water is defined as having a total dissolved solids (TDS) content between 1,000 and 10,000 parts per million, compared to seawater, which has about 35,000 ppm. In Champaign County, the Mahomet Aquifer has TDS levels on the order of 350 – 400 ppm. There is a secondary, non-enforced, drinking water standard of 500 ppm; at higher TDS concentrations, the water begins to taste salty.

Desalination of seawater is being done in a number places in the world, but it tends to be expensive, energy intensive, and produces brine that must be disposed of carefully. Desalination so far has only made sense in arid regions with very limited freshwater resources, such as Israel, Australia, and Saudi Arabia, which has the largest desalination project in the world. Cape Coral, Florida, was the first U.S. municipality to desalinate seawater. El Paso, Texas, has been desalinating brackish groundwater since 2004; the cost is about twice the cost of extracting and treating fresh groundwater.

Illinois has lots of brackish groundwater, primarily in bedrock aquifers, but I know of no plans to desalinate it. These bedrock aquifers, primarily sandstones, are important aquifers in northern Illinois (as well as Wisconsin, Iowa, and Minnesota), but the water quality degrades as you head south into the interior of the Illinois Basin. TDS levels can reach many times the salinity of seawater in some of these formations in the southern half of Illinois.