Desalination is a hot topic. As our state’s population grows and drought continues to impact water supplies, more communities are diversifying their water supply sources and exploring desalinating seawater and brackish water for drinking water.
In the 2022 State Water Plan, the recommended desalination strategies nearly doubled from the 2017 State Water Plan. If all the recommended brackish groundwater desalination projects are implemented from the 2022 State Water Plan, brackish groundwater desalination would provide 157,000 acre-feet per year in 2070, an increase of 42 percent from the 2017 plan. If all the recommended seawater desalination projects are implemented, they would provide 192,000 acre-feet per year in 2070, an increase of 66 percent from the 2017 plan.
The desalination program at the Texas Water Development Board (TWDB) began as part of Governor Rick Perry’s 2002 seawater desalination initiative to evaluate desalinated seawater as a potential drinking water source. Shortly thereafter, this program expanded to include brackish water desalination as another potential alternative water source. This initiative led the TWDB to fund grants to advance desalination that resulted in guidance documents, white papers, and reports on planning, permitting, and research.
“The TWDB continues hosting and updating a desalination plant database, staying updated on the latest desalination technologies and practices, producing a biennial legislative report, and providing technical assistance to a variety of stakeholders including water managers, engineers, and researchers,” said Erika Mancha, Director of the Conservation and Innovative Water Technologies Division at the TWDB.
What is desalination?
Put simply, desalination is a process that removes dissolved mineral salts and other impurities to make saline and brackish water suitable for humans to drink. The two most common methods are thermal desalination and membrane-based desalination.
- Thermal desalination involves heating saline water to produce water vapor, which is then condensed and collected as fresh water.
- Membrane technologies, such as reverse osmosis and electrodialysis reversal, use semi-permeable membranes to separate salts from water.
- Reverse osmosis uses high-pressure pumps to push saline water through membranes that allow smaller water molecules to pass while rejecting larger salt minerals, resulting in desalinated water and brine.
- Electrodialysis reversal uses alternating ion-exchange membranes and electrodes to separate water from dissolved salts.
There are several treatment processes involved in desalination, including pretreatment to filter out solids and condition the water, removal of salts and other minerals, and post-treatment to prepare the desalinated water for distribution. The brine is disposed of through various methods, such as surface water discharge, deep well injection, or release into municipal sewer systems.
The most common method for desalination is reverse osmosis, which most municipal desalination plants in Texas currently utilize for municipal water supplies.
Water desalination plants operating in Texas
Many people recognize the need to expand our state's water supply network but may be surprised to learn that 60 municipal desalination plants are already operating in Texas. Right now, those plants desalinate brackish groundwater, brackish surface water, or reclaimed water and have a combined design capacity of approximately 172 million gallons per day. Of the 60 facilities, 43 desalinate brackish groundwater with a combined capacity of 98 million gallons per day.
Desalinating brackish groundwater
Many people may envision seawater when they think of desalination, but it’s also possible to desalinate water from beneath our feet. Groundwater becomes brackish when the water dissolves minerals as it percolates through an aquifer.
Brackish groundwater is usually less saline than seawater but has a higher salt content than freshwater, and there’s quite a bit of it in Texas. Our state is estimated to have more than 3 billion acre-feet of brackish groundwater in most major and minor aquifers.
That’s why desalination is being considered and implemented by large and small communities alike. Large-scale brackish groundwater desalination plants currently operate in El Paso, San Antonio, and the Rio Grande Valley. The Kay Bailey Hutchison Desalination Plant in El Paso is home to the world's largest inland desalination plant that can produce up to 27.5 million gallons of fresh water daily. Most brackish groundwater desalination plants in Texas are smaller—like the plants in Evant, Hubbard, Bardwell, Kenedy, and Fort Stockton.
While the TWDB estimates a large volume of brackish groundwater in Texas aquifers, not all of this water is recoverable. Future projects will require further study at the site scale to better understand long-term availability. The Brackish Resources Aquifer Characterization System (BRACS) program at the TWDB was established by the legislature to map and characterize brackish groundwater to further refine our estimates of total volumes in place and identify zones with the highest potential for long-term production with minimal risk of adverse impacts. Visit the TWDB’s BRACS program website for more information.
Desalinating brackish surface water and reclaimed water
In addition to brackish groundwater, facilities in Texas also desalinate brackish surface water and reclaimed water. Brackish surface water has a higher salt content than freshwater but less than seawater. Sixteen Texas facilities use brackish surface water as a source of raw water, accounting for up to 71 million gallons per day. Most brackish surface water desalination plants are along the upper portions of the Brazos and Colorado rivers.
A third and less common use of desalination technology involves treating reclaimed water. Desalinated reclaimed water can supplement existing water supplies, reducing reliance on traditional sources. The nation’s first direct potable reuse facility is in Big Spring, Texas. The advanced treatment process at the Big Spring plant includes microfiltration, reverse osmosis, and ultraviolet purification.
Seawater desalination is on the horizon
Governor Rick Perry directed the TWDB in 2002 to develop a proposal to build Texas' first large-scale seawater desalination plant to produce drinking water. The following year, the Texas Legislature passed House Bill 1370, directing the agency to advance the development of cost-effective water supplies from seawater desalination in the state. The governor and legislators recognized the need for a drought-proof water source, and the 370-mile-long coastline of the Texas Gulf Coast provides access to an infinite volume of seawater.
Now, Corpus Christi and the Laguna Madre Water District hope to introduce seawater desalination to Texas. Corpus Christi’s Inner Harbor Water Treatment Plant would convert bay water into fresh drinking water. Farther south, the Laguna Madre Water District has plans to build a seawater desalination plant in Port Isabel using water from the Brownsville Ship Channel.
In addition to creating a new fresh water supply, seawater desalination plants along the Texas Gulf Coast would relieve stress on existing conventional surface water and groundwater supply sources in coastal areas.
Factors in considering desalination
A desalination plant's location is a big factor in determining where to dispose of the main byproduct of desalination, known as brine or concentrate. Surface water bodies, evaporation ponds, land application, deep well injection, or wastewater treatment plants are concentrate disposal options for inland desalination plants. Seawater desalination plants must carefully discharge brine into the ocean to minimize impact to coastal ecosystems.
Compared to other water sources, desalination can be expensive. The cost depends on several factors, including source water, location, treatment process, and plant size. Brackish water costs less to desalinate than seawater because brackish water is less salty and contains fewer total dissolved solids, which reduces energy requirements to separate dissolved salts from water. The TWDB estimates that, in general, the cost of desalinated brackish water can range from $1.25 to $2.60 per 1,000 gallons, whereas desalinated seawater may cost anywhere from $3.60 to $5.80 per 1,000 gallons.
TWDB financial assistance programs can help communities implement desalination projects. To date, the TWDB has helped finance 52 desalination projects in Texas through $1.18 billion in financial assistance commitments.
Visit the TWDB website to learn more about desalination in Texas and the agency’s programs.
