There’s a great deal of talk and debate about the value of treating brackish water, or water that is more saline than fresh water, but not quite as saline as seawater. Brackish water can result from the mixing of seawater with fresh water, as in surface waters such as estuaries or other watery ecosystems, or it can occur underground in aquifers.
Although these definitions may seem vague, there are some precise definitions for salty waters. These vary based on the concentration of salt in the water. For example, Daniel Hillel, writing in Salinity Management for Sustainable Irrigation: Integrating Science, Environment, and Economics, gives these as:
Designation, total dissolved salts (ppm):
- Fresh water, <500
- Slightly brackish, 500-1,000
- Brackish, 1,000-2,000
- Moderately saline, 2,000-5,000
- Saline, 5,000-10,000
- Highly saline, 10,000-35,000
- Brine, >35,000
The U.S. Geological Survey (USGS), however, defines water salinity without a specific designation for brackish water. It bases its definitions on these values:
Designation, total dissolved salts (ppm):
- Fresh water, <1,000
- Slightly saline water, 1,000 ppm to 3,000
- Moderately saline water, 3,000 ppm to 10,000
- Highly saline water, 10,000 ppm to 35,000
However it’s defined, the problem is there is a lot of salty water available worldwide that needs proper treatment in order to become potable. The USGS notes:
There is an extensive amount of very salty water in the ground in the western United States. In New Mexico, approximately 75 percent of groundwater is too saline for most uses without treatment. Water in this area may have been leftover from ancient times when saline seas occupied the western U.S., and, also, as rainfall infiltrates downward into the ground, it can encounter rocks that contain highly soluble minerals, which turn the water saline. Groundwater can exist and move for thousands of years and can thus become as saline as ocean water.
Texas, for example, has abundant underground water, including 880 trillion gallons of primarily brackish groundwater. State officials are struggling to define “brackish” to better conserve those supplies. (Some lawmakers recently sought to have it be defined as any water with a level of total dissolved solids between 1,000 and 10,000 milligrams per liter.) The Texas Tribune explained:
Hundreds of trillions of gallons of brackish water are estimated to lie underneath Texas. […] There are just a few problems with the water: It has too much salt and other dissolved solids to be fit to drink, treating it carries a significant expense, and regulating its withdrawal – like with all Texas groundwater – has already proved to be tricky.
Therefore, the problem in some areas is not water quantity, but water quality. Brackish water is used in some areas of the world for irrigation, but most industries can’t use it since the solids could damage equipment. It’s not good for livestock or human consumption.
Because freshwater wells — which are often the source of municipal drinking water — draw from groundwater supplies, contamination by saline water poses a threat to city drinking water supplies, particularly near coastlines.
The problem is seen worldwide. Roughly half of the world’s population lives within 200 km of a coastline. Areas already experiencing saltwater intrusion include coastal New Jersey, Florida, and New York in the U.S., as well as cities along the Laizhou Gulf in China; Manila, Philippines; and Perth, Australia. In the Maldives, the island of Thoddoo is using a combination of rainwater harvesting and desalination to protect its aquifers from overexploitation.
The Maldives is a good example of a populated island in need of potable public water supplies. Often the available feed water in island communities is both saline and brackish, depending on the source. Well water, for example, is frequently brackish.
Another example can be found on the island nation of Cyprus, where groundwater supplies for the city of Limassol were too brackish for drinking, and had high nitrate levels. Fluence constructed a desalination plant at Garillis for Cyprus Water Development that uses brackish water reverse osmosis to produce 10 million L/d of high-quality drinking water. Learn more about the plant in this short video.
Desalinated brackish water is not only used for drinking water. Salty water pumped from underground sources is being used for cooling by power generators in the U.S. In 2005, more than 95 percent of the saline water drawn from groundwater storage was used by the thermoelectric-power industry. The remaining 5 percent was used for mining and industrial tasks.
The Pacific Rubiales oilfield is a prime example of the use of brackish water reverse osmosis in the petrochemical industry. Feed water from the field is brackish and also typically contains residual oils, hydrocarbons, solids, and other contaminants. All of these impurities must be removed before any desalination process can take place. This facility uses three stages of reverse osmosis. Treated water is reused for irrigation, with about 10 percent reinjected into the aquifer.
Advanced treatment technologies are needed for purifying and desalinating brackish groundwater. Among the technologies applied to this type of source water are reverse osmosis and ultrafiltration, as well as other membrane-based technologies.
Relieving Water Scarcity
Brackish water desalination has filled the need for an alternative fresh water source in some areas of the U.S. where seawater desalination has been controversial and has been challenged by officials or the public. In California, for example, 17 brackish water desalination plants with a combined capacity of 252,000 m3/d were in development as of 2017.
Because brackish water can be treated to provide a source of healthy, reliable drinking water, more companies and communities are investigating brackish water desalination as a practical means to avert water scarcity.
The cost of desalination continues to decrease. Technologies such as reverse osmosis and energy recovery are making production more effective and energy-efficient. And containerized desalination solutions like Fluence’s NIROBOX™ allow for treatment without a large capital investment in infrastructure.
Could brackish water desalination be the solution to your water needs? Contact Fluence to speak to our experts.