- I often hear terms like brackish water, saline water, seawater, and brine in reference to desalination. What is the difference between them?
- What is the average unit cost of desalinated brackish groundwater?
- How long does it take to build a plant, from the permit phase to the final construction phase?
- How many brackish groundwater desalination plants are currently in operation in Texas?
- How many brackish water desalination plants are there in the United States? Where are most of them located?
- What are the most common concentrate management methods being used by brackish desalination plants in Texas?
- Are there alternative energy sources being used to power brackish water desalination plants in Texas?
- What are the major activities that use desalinated brackish groundwater in Texas and what is the range of TDS concentrations in the feedwater?
- Is the use of desalinated groundwater an increasing or decreasing trend?
- What is the biggest benefit of using desalinated groundwater?
- What is the biggest challenge (technical or economical) in developing and using desalinated brackish groundwater in Texas?
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 2, below).
2. What is the average unit cost of desalinated brackish groundwater?
Desalinated water cost is a function of capital costs, debt service, and operating costs. In general, desalinated brackish water can cost about $1.50 per 1,000 gallons.
3. 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 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.
4. How many brackish groundwater desalination plants are currently in operation in Texas?
Currently, there are 35 municipal desalination plants in Texas with a design capacity of >0.023 million gallons per day.Collectively, these plants have a capacity of approximately 85 MGD (Source: TWDB Desalination Plant Database, 2017).
In 2012, there were 34 desalination plants in Texas with a total capacity of approximately 73 MGD (Source: TWDB Desalination Plant Database, 2012). An additional 50 municipal desalination plants with a design capacity of <0.023 MGD exist that are small units (Nicot and others, 2006; 1.29 MB).
5. How many brackish water desalination plants are there in the United States? Where are most of them located?
There are about 325 brackish groundwater desalination plants in the United States. Almost half of them (45 percent) are in Florida, 14 percent in California, and 9 percent in Texas (Mickley and others, 2011 and Nicot and others, 2005).
6. What are the most common concentrate management methods being used by brackish desalination plants in Texas?
Based on information collected from 38 public drinking water facilities that desalinate brackish groundwater, about 37% of the plants discharge to a surface water body, 24% to a municipal sewer, 21% discharge to an evaporation pond, and about 13% utilize land application. About 5% remain unknown. More information on these disposal methods is available in A Desalination Database for Texas (Nicot and others, 2006).
Additionally, we know of at least one facility (the 27.5 MGD Kay Bailey Hutchison Desalination Plant) that is using deep well injection (USEPA Class V injection well) to dispose off concentrates from desalination. It the first plant in Texas to use this disposal option. The plant came online on August 8, 2007.
7. Are there alternative energy sources being used to power brackish water desalination plants in Texas?
We are not aware of any existing desalination plants in Texas that are being powered by alternative sources of energy such as wind, solar, bio-fuels, etc. However, we recently funded a pilot-scale brackish groundwater desalination demonstration project in Seminole, Gaines County that will use electricity generated by wind to power the desalination system and pumps.
8. What are the major activities that use desalinated brackish groundwater in Texas and what is the range of TDS concentrations in the feedwater?
While we have a relatively accurate estimate of the number of desalination plants (and their capacity) supplying potable water (municipal supply) to Texans, our information on the use of desalinated water for industrial purposes is less accurate. According to an estimate by the International Desalination Association (IDA, 2001), Texas has a total desalination capacity of about 100 MGD. Of this, about 53 MGD is being produced for municipal use (A Desalination Database for Texas, 2006; 1.29 MB) and about 47 MGD for industrial use. Surface water accounts for about 25 MGD of municipal supplies and groundwater about 28 MGD.
Steam-generation probably accounts for about 30 to 45-MGD of industrial capacity, 10-MGD for the food and beverage industry, and about 15 to 30-MGD for the semiconductor industry.
Collecting water usage data in Texas from industrial facilities using desalination has proven to be notoriously difficult and we ask that the information provided above be used with caution.
The total dissolved solids (TDS) concentrations of feedwater used in municipal-use desalination plants range from 470 milligrams per liter (mg/l) to about 3,800 mg/l.
9. Is the use of desalinated groundwater an increasing or decreasing trend?
The use of desalinated groundwater is expected to grow in the future. According toIn the 2022 State Water Plan, ten regional water planning groups recommended desalination (including brackish groundwater, seawater, and surface water desalination). If implemented, desalination would produce about 412,000 acre-feet per year of additional water supplies by 2070. This constitutes about 5.4 percent of all recommended water management strategies in the state water plan. Approximately 157,000 acre-feet per year of supply will be from brackish groundwater desalination, 192,000 acre-feet per year of supply from seawater groundwater desalination, and 63,000 acre-feet per year of supply from surface water desalination.
10. What is the biggest benefit of using desalinated groundwater?
The biggest benefit of using desalinated groundwater in Texas is the preservation of our dwindling fresh water aquifers. The population of Texas is expected to increase more than 70 percent within the next 50 years and water demand to increase almost 17 percent in that time period. During that same time period, existing water supplies (volume of water that can be produced with current permits and existing infrastructure) is expected to decrease about 11 percent.
11. What is the biggest challenge (technical or economical) in developing and using desalinated brackish groundwater in Texas?
Cost is the biggest hurdle to the more widespread use of desalinated groundwater. Nevertheless, the cost of desalinating brackish groundwater is becoming more competitive and several communities such as those in the Lower Rio Grande Valley are already using desalinated water on a regular basis for their municipal supply.