The Texas Water Development Board (TWDB) is warning that “[a]ccess to adequate supplies of fresh water is fast becoming critical in many parts of the world. Texas is in a similar situation. With a population expected to double in the next 50 years, Texas faces a growing demand for fresh water.” In a report titled “Brackish Groundwater in Texas,” authors Sanjeev Kalaswad, Brent Christian, and Rima Petrossian of the TWDB explain that “[f]ortunately, the State has a large reserve of brackish groundwater that may be available for use after treatment.” Estimates vary, but it is believed that Texas could have anywhere from 2.7 billion to 3.2 billion acre-feet of brackish groundwater in aquifers throughout the state. To put that in perspective, Houston’s Drinking Water Operations (DWO) Branch produces and distributes a little over half a million acre-feet of water per year to its customers.
According to the United States Geological Survey, brackish water is “water that has a greater dissolved-solids content than occurs in freshwater, but not as much as seawater … All water naturally contains dissolved solids that, if present in sufficient concentration, can make a surface-water or groundwater resource “brackish,” typically defined as distastefully salty.” However, brackish water should not be strictly understood as “distasteful” or “salty.” It really depends on the mineral content, which is quantified using a standard unit of measure called “total dissolved solids” (TDS) in milligrams per liter. For folks in the Big Bend, the crystal-clear, spring-fed pool at Balmorhea State Park is perhaps the most tangible example of brackish groundwater in all its glory. The Bureau of Economic Geology defines the mineral content there as > 2,000 mg/L TDS.
The state has been studying the quality and quantity of the brackish groundwater supply through a program called the Brackish Resources Aquifer Characterization System (BRACS). Established in 2008 with funding from the Texas Legislature, BRACS is intended to characterize the brackish aquifers throughout the state. This can involve “evaluating available water well records, geophysical well logs, and geologic reports … mapping the water-bearing portions of the aquifer and their hydraulic properties, [and] estimating salinity from water well records and geophysical well logs [to estimate] volumes of brackish groundwater,” according to the TWDB website. In 2015, the Legislature also directed TWDB to “identify and designate brackish groundwater production zones in the state … determine the volumes of groundwater that a brackish groundwater production zone can produce over 30- and 50-year periods without causing significant impact to water availability or water quality … [and] … make recommendations on reasonable monitoring to observe the effects of brackish groundwater production within the zone.”
The TWDB report distinguishes between brackish water in the “1,000 to 3,000 mg/L TDS category” and the “3,000 to 10,000 mg/L TDS category.” A 2003 study conducted by LBG-Guyton Associates for the TWDB suggests that the statewide volume of groundwater in the lower TDS category “is roughly twice as much as the volume in the 3,000 to 10,000 mg/L” category. This is good news for brackish water as a “new” water source because the lower the TDS content, the easier and cheaper it is to treat the water to agricultural or potable quality using a process called desalination.
While too costly for regions where fresh surface and groundwater are readily available, brackish water desalination is looking increasingly feasible in areas where water shortages are becoming the norm. “It’s usually only when communities start to run out of freshwater that they start to look at brackish water,” Kalaswad told the Texas Water Resources Institute in its report titled “Everybody is talking about it: Is brackish groundwater the most promising ‘new’ water?” If drought conditions persist, Kalaswad predicted that Texas could use even more brackish groundwater for future water supplies than currently projected. “The technology is there,” he said. “It’s just a matter of availability of the resource and how much people are willing to pay for water.”
State Sen. Charles Perry, chairman of the Senate Committee on Water, Agriculture, and Rural Affairs in the Texas Senate, is among the biggest proponents of brackish groundwater as a “new” source of water for the state. He has filed several bills this session aimed at reducing the state’s reliance on freshwater aquifers, with the “broader goal of developing non-traditional water sources, including brackish groundwater, to satiate Texas’s growing thirst for water supply and alleviate much of the existing, often increasing pressure on the state’s non-saline groundwater sources,” according to Perry’s Committee Director Andrew Parks. Earlier this year, Perry told the Texas Observer that “the desal cost on the … brackish side is significantly lower than what it was just 10 years ago. So technology keeps advancing.”
The city of El Paso currently operates America’s largest inland desalination plant, which uses raw brackish water to produce around 27.5 million gallons of potable-grade drinking water a day. This desalinated water is 2.1 times more expensive than fresh groundwater and 70% more expensive than surface water, but around half that cost is due to the energy required for treatment. The key to brackish groundwater as a “new” source of supply for Texas will be reducing the energy costs associated with its treatment.
Trey Gerfers serves as general manager of the Presidio County Underground Water Conservation District. A San Antonio native, he has lived in Marfa since 2013 and can be reached at tgerfers@pcuwcd.org.