Seawater FAQs
Also see Brackish FAQ and General FAQ
- I often hear terms like brackish water, saline water, seawater, and brine in reference to desalination. What is the difference between them?
- How can water users not located on the coast benefit from desalinated seawater?
- Of the three projects that TWDB recommended for future studies (Brownsville, Corpus Christi and Freeport), would the TWDB select one to recommend to the Governor, based on the results of the feasibility studies?
- What is the average unit cost of desalinated 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?
- What happens to the salt that is removed from the water during desalination?
- How will desalinated seawater reach non-coastal areas for use?
- How will seawater desalination projects be funded?
- How many seawater desalination plants are currently in operation in Texas?
- How many seawater desalination plants are there in the United States? Where are most of them located?
Answers to Frequently Asked Questions
1. 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. And, brine is very salty water (TDS greater than 35,000 mg/l). Seawater typically is very salty (TDS >35,000 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 4, below).
2. 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.
3. Of the three projects that TWDB recommended for future studies (Brownsville, Corpus Christi and Freeport), would the TWDB select one to recommend to the Governor, based on the results of the feasibility studies?
In 2003, TWDB funded $1.5 million for feasibility studies to assess the technical viability of these three proposed projects. These studies concluded that all three proposed projects were technically feasible and outlined the financial requirements necessary to implement the projects. In 2004, TWDB considered these conclusions and recommended that the state continue advancing toward implementation of a large-scale demonstration seawater desalination facility in Texas. In spring 2006, TWDB approved funding for a pilot plant study in Brownsville (Brownsville PUB). The 12-month study began in fall 2006 and is expected to be completed in late 2008.
4. What is the average unit cost of desalinated seawater?
Desalinated water cost is a function of capital costs, debt service, and operating costs. In general, desalinated seawater may cost anywhere from $2.50 to $3.00 per 1,000 gallons or more.
5. 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. Texas does not yet have a seawater desalination plant, but using an example of a large brackish groundwater desalination plant (the El Paso-Fort Bliss plant) that is presently under construction it may take at least 5 years. Planning for the 27.5-MGD 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 it was opened in August 2007.
6. 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.
7. What happens to the salt that is removed from the water during desalination?
It 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.
8. 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.
9. How will seawater desalination projects be funded?
The state financial assistance programs, federal appropriations, and private participation may be used for funding desalination projects.
10. How many seawater desalination plants are currently in operation in Texas?
At present, there are no seawater desalination plants in Texas although two pilot plant studies are currently being conducted in the lower Rio Grande Valley (Brownsville PUB and Laguna Madre Water District). It is likely that a full-scale plant will result from one of these studies.
11. How many desalination 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 (114) are in Florida, 33 in California, and 38 in Texas (Mickley, 2004 and Nicot and others, 2006 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 10, above) as is California which is proposing about two dozen plants along the Pacific coast.