- What is desalination?
- I often hear terms like brackish water, saline water, seawater, and brine in reference to desalination. What is the difference between them?
- Why is desalination an important issue in Texas today?
- How can water users not located on the coast benefit from desalinated seawater?
- If an entity wishes to build a desalination plant and does not need state funding, does the TWDB have a say in whether or not it gets built?
- How are the impacts to the environment considered in the development of desalination projects?
- How much does desalination cost?
- What is the average unit cost of desalinated brackish groundwater? Seawater?
- How long does it take to build a plant, from the permit phase to the final construction phase?
- Does desalinating seawater hurt the marine life in the ocean?
- How will desalination affect the Regional and State Water Plans?
- What happens to the salt that is removed from the water?
- How will desalinated seawater reach non-coastal areas for use?
- If desalination plants become widespread, could Texas avoid having to build news dams and reservoirs to meet water needs in the future?
- How will seawater desalination projects be funded?
- How many brackish groundwater desalination plants are currently in operation in Texas? How many seawater desalination plants?
- How many desalination (brackish water and seawater) plants are there in the United States? Where are most of them located?
- Are there desalination plants in other countries?
- Whom can I contact at the TWDB for more information about desalination and desalination projects?
Answers to Frequently Asked Questions
1. What is desalination?
Desalination is the process of removing dissolved salts from water. The two most common desalination technologies are thermal and membrane technologies. The thermal process involves heating saline water to produce water vapor which is then condensed and collected as fresh water. Membrane processes rely on semi-permeable membranes to separate salts from water. Membrane processes can be pressure-driven (reverse osmosis or RO, the most common method used in desalination), or voltage-driven (electrodialysis and electrodialysis reversal).
2. I often hear terms like brackish water, saline water, seawater, and brine in reference to desalination. What is the difference between them?
The primary difference between the types of water mentioned above is in the amount of total dissolved solids (TDS) they contain. Brackish water typically contains TDS in concentrations ranging from 1,000 milligrams per liter (mg/l) to 10,000 mg/l. Saline water or salt water has more than 10,000 mg/l TDS. Seawater typically is very salty (TDS >35,000 mg/l). Brine contains dissolved minerals and other contaminants that are removed from the water during desalination. TDS concentration of brine is also very high (>10,000 mg/L).
In a reverse-osmosis system, the greater the TDS concentration of the water, the higher the pressure needed for the pumps to push water through the membranes, and consequently, the higher the energy costs. Desalinating seawater is, therefore, usually more costly than desalinating brackish water (see Question 8, below).
3. Why is desalination an important issue in Texas today?
The increasing demand for water, coupled with the state’s vulnerability to drought events, has compelled water planners to consider all potential sources of water in their planning efforts. In April 2002, Governor Rick Perry directed the Texas Water Development Board to develop a recommendation for a large-scale seawater desalination demonstration project. The Governor’s vision is to procure a drought-proof source of water for all Texans.
The 370-mile-long coastline of the Texas Gulf Coast provides access to an infinite volume of seawater for desalination. Recent advances in membrane technology have lowered desalination production costs making seawater desalination a more competitive option along the coast. Inland, more than 2.7 billion acre-feet of brackish groundwater is present in the aquifers of the state, providing yet another potential source of water for desalination.
4. How can water users not located on the coast benefit from desalinated seawater?
Development of seawater desalination along the Texas Gulf Coast will help relieve stress on existing conventional surface water and groundwater supply sources in coastal areas which in turn could make these resources available to water users located away from the coast. In this context, seawater desalination can indirectly benefit people living hundreds of miles away from the coastline.
5. If an entity wishes to build a desalination plant and does not need state funding, does the TWDB have a say in whether or not it gets built?
The TWDB does not have regulatory authority. However, the TWDB’s financial assistance programs are tools to support the development of water management strategies identified in the Regional and State Water Plans rather than as a permitting process. Projects submitted for TWDB funding must demonstrate consistency with those plans.
Regardless of the funding mechanism, a whole host of local, state, and federal permit requirements apply to desalination plants, and appropriate permits must be obtained by the entity seeking to build the plant before construction can begin. An overview of a permitting roadmap for seawater desalination facilities in Texas using reverse osmosis processes ( 2.63 MB) is available in TWDB Report 363.
6. How are the impacts to the environment considered in the development of desalination projects?
As with any major construction project, an Environmental Impact Statement (EIS) is required for a desalination plant prior to construction. EIS studies are conducted to identify and investigate possible impacts of disposing waste on the state’s soil, air, and water resources and to recommend steps to avoid or reduce these impacts. EIS studies are the responsibility of the project owners.
7. How much does it cost to build a desalination plant?
It depends on several factors including source water, location, treatment process, and the size of the plant. Building a brackish water desalination plant usually costs less than that of a seawater desalination plant because brackish water is generally cleaner and contains less total dissolved salts (see Question 2, above). In 2007, $87 million was spent to build the Kay Bailey Hutchison brackish groundwater desalination plant in Texas. Design capacity of the KBH plant is 27.5 million gallons per day (MGD). The 2010 biennial report on seawater desalination projected that it will cost approximately $32 million to build a 2.5 MGD seawater desalination plant, and approximately $658 million to build a 100 MGD seawater desalination plant in Texas.
Additional information on the cost of desalination plants in Texas is available at http://www.twdb.texas.gov/innovativewater/desal/doc/Cost_of_Desalination_in_Texas.pdf
8. What is the average unit cost of desalinated brackish groundwater? Seawater?
Unit cost of desalinated water is a function of capital cost, debt service, and operating cost. In general, 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. Additional information on the cost of desalination plants in Texas is available at http://www.twdb.texas.gov/innovativewater/desal/doc/Cost_of_Desalination_in_Texas.pdf
09. How long does it take to build a plant, from the permit phase to the final construction phase?
The time required for full implementation of a desalination plant varies from project to project. Obviously, it depends on the size and complexity of the plant, and whether it has to be built from scratch or can use existing water intake structures. As an example, planning for the 27.5-MGD Kay Bailey Hutchison Brackish Groundwater Desalination Plant started in 2001, a draft Environmental Impact Statement was completed in July 2004, construction of the plant commenced in early spring 2005, and the construction was completed in 2007.
10. Does desalinating seawater hurt the marine life in the ocean?
Desalinating seawater involves some processes that could impact marine life. However, those impacts can be avoided or minimized by implementing environmental safeguards at every phase of the project from planning its location to operating it in a manner that results in acceptable water quality and brine loading at the discharge. For example, intake of seawater can entrain marine life, but screens placed at intake locations at power plants and industrial facilities have successfully demonstrated that this type of impact can be significantly reduced. An Environmental Impact Statement for such a desalination project will need to consider and evaluate all potential impacts to the environment, and identify the best management practices to eliminate or reduce adverse impacts.
11. How is desalination considered in the Regional and State Water Plans?
Continued improvements in desalination technologies and the associated decrease in costs have made desalination a practical and cost-effective alternative source of water supply in Texas. It is now routinely considered in the regional water planning process as a tool to meet future water needs.
In the 2011 Regional Water Plans, six of 16 regional water planning groups recommended desalination as a water management strategy to meet at least some of their projected water need. In total, recommended desalination projects would create about 309,782 acre-feet per year of new water supplies by 2060, with 59 percent of this water coming from brackish water desalination and 41 percent coming from seawater desalination.
12. What happens to the salt that is removed from the water?
In reverse osmosis, salt water on one side of a semi-permeable membrane is subjected to pressure, causing fresh water to diffuse through the membrane leaving behind a concentrate stream. The concentrate stream contains the majority of the dissolved minerals and other contaminants, which needs to be safely disposed off.
Concentrate management can become one of the most important factors in determining the feasibility of a plant. Concentrate produced during seawater desalination can be disposed through deep well injection on land or returned to the ocean in a controlled process to avoid detrimental effect to the environment or marine life. For concentrates produced in inland facilities, a few other options exist. These include disposal to surface water bodies, evaporation ponds, or to wastewater treatment plants. In some instances, the concentrate can also be utilized beneficially for industrial processes.
13. How will desalinated seawater reach non-coastal areas for use?
Desalinated seawater could be piped directly to non-coastal customers using existing or new pipelines. Potentially, once desalinated seawater becomes available in the coastal areas, there would be a ripple effect benefit for the environment and water users located away from the coast.
14. If desalination plants become widespread, could Texas avoid having to build news dams and reservoirs to meet water needs in the future?
Seawater and brackish groundwater desalination are one of many tools in the State’s long-term water supply toolbox. Whether desalination will replace, supplement, or complement other technologies will depend to a large extent on its affordability and the availability of the raw resource (brackish groundwater or seawater) close to areas of expected shortages.
15. How will seawater desalination projects be funded?
The state financial assistance programs, federal appropriations, and private participation may be used for funding desalination projects.
16. How many brackish groundwater desalination plants are currently in operation in Texas? How many seawater desalination plants?
There are 44 desalination plants in Texas with a design capacity of >0.025 million gallons per day (MGD) that are part of the public water supply (PWS) system. Collectively, these plants have a capacity of approximately 120 MGD. An additional 50 PWS desalination plants with a design capacity of <0.025 MGD each, produce less than 0.5 MGD (Nicot and others, 2005; 1.29 MB). Many of these are small units.
At present, there are no seawater desalination plants in Texas. However, in spring 2011, voters in the Laguna Madre Water District, which serves South Padre Island, Port Isabel and the surrounding area, authorized issuance of a bond to fund a full-scale sea water desalination plant. Laguna Madre Water District has not set a date for construction of the facility.
17. How many desalination (brackish water and seawater) plants are there in the United States? Where are most of them located?
There are about 250 desalination plants in the US with a design capacity of >0.025 MGD. Almost half of them (155) are in Florida, 49 in California, and 44 in Texas (Mickley, 2004 and Nicot and others, 2005 1.29 MB). The 25-MGD desalination plant at Tampa Bay, Florida, is so far, the largest seawater desalination plant in the country. Texas is planning to build a seawater desalination plant within the next several years (see Question 17, above) as is California which is proposing about two dozen plants along the Pacific coast.
18. Are there desalination plants in other countries?
Yes, there are about 12,500 desalination facilities located in 120 countries worldwide with a total capacity of about 4 BGD (billion gallons per day). Almost 60 percent of these plants are located in the Middle East where desalinated water accounts for more than 70 percent of the region’s water supply. For more information on desalination plants in the Middle East, visit the Middle East Desalination Research Center Web site.
Other countries such as Australia, Singapore, India, the United Kingdom, and several countries in the Caribbean also either presently have or are planning to build desalination plants. Recently, the government of Spain announced plans to build a total of 21 seawater desalination plants along the coast of the Mediterranean Sea. These plants will have a combined capacity of approximately 527,000 acre-feet per year, equal to the present capacity of the 900 existing plants in the country.
19. Whom can I contact at the Texas Water Development Board for more information about desalination and desalination projects?
If you have any general questions about desalination including policy or legislative issues, or need information on TWDB’s seawater desalination projects, please contact Jorge Arroyo (512-475-3003).
Sanjeev Kalaswad (512-936-0838) and Jorge Arroyo (512-475-3003) manage TWDB’s brackish groundwater desalination project contracts.