Brackish Water Desalination: Turning Salty Groundwater Into Supply
By Sean Alford, Permitting Plus
Brackish water desalination takes groundwater that is too high in salt to drink or to use in a process, usually 1,000 to 10,000 milligrams per liter of dissolved salts, and runs it through reverse osmosis membranes to make fresh water. It is cheaper than ocean desalination on energy and equipment, because the water is far less salty. It is harder on one point: the brine has no sea to go to.
For inland communities, industrial sites, and agricultural regions sitting over saline aquifers, inland desalination is often the only new water supply available. Texas, the American Southwest, the Middle East, North Africa, and parts of Asia are all building it. The question is rarely whether it works. It is where the concentrate goes and what the aquifer will look like in twenty years.
Permitting Plus helps companies and communities plan, permit, and set up desalination systems, including saline groundwater plants. This article covers what brackish water reverse osmosis involves, its applications, how it differs from seawater, what it costs, and what the regulator asks. Our desalination page covers our approach to desalination projects as a whole.
Table of Contents
What brackish water is
This water sits between fresh and seawater. Fresh water has less than about 1,000 milligrams per liter of total dissolved solids. The ocean has around 35,000. Brackish water is everything in between, and most groundwater used for inland desalination is in the 1,000 to 10,000 range.
The salts in saline groundwater are not the same as those in the ocean, which is dominated by sodium chloride. Brackish aquifers carry whatever the rock gave them: sodium, chloride, sulfate, calcium, magnesium, bicarbonate, and often silica, iron, manganese, boron, or arsenic. That chemistry decides the treatment, the recovery, and the brine, which is why the water analysis comes before anything else.
Where brackish groundwater is found
Saline aquifers underlie large parts of the United States, especially Texas, New Mexico, Arizona, California, Florida, and the High Plains. Texas alone has an estimated 2.7 billion acre-feet of saline groundwater in its aquifers, according to the Texas Water Development Board, and has built dozens of inland desalination plants to use it. Similar saline aquifers exist across the Middle East, North Africa, Australia, and inland Asia, and communities there face the same concentrate question. Coastal aquifers that have been over-pumped often turn brackish through seawater intrusion, which is a growing driver in coastal cities.
Brackish desalination in Texas
Texas is the clearest example of a state building its water future on saline groundwater, and it is where most of the American experience with inland desalination has been earned. What Texas has learned applies well beyond Texas.
The Texas Water Development Board, known as the TWDB, the state agency that plans Texas water supplies, estimates that Texas aquifers hold about 2.7 billion acre-feet of saline groundwater, roughly 880 trillion gallons, against fresh groundwater supplies that are shrinking in many parts of the state. By the TWDB’s count, Texas has more than fifty municipal desalination plants, most of them on saline groundwater, producing well over a hundred million gallons a day of drinking water for Texas communities, and plants of a few hundred thousand gallons a day serve small communities across the state. The largest inland desalination plant in the United States is in El Paso, Texas, producing up to 27.5 million gallons a day, about 104,000 cubic meters, from the Hueco Bolson aquifer. San Antonio’s water utility runs a large groundwater desalination plant drawing on the Wilcox aquifer, and communities across South Texas and the Texas Gulf Coast run smaller ones.
The Texas approach, built largely by the state water board, has three parts that other states are copying. A state saline groundwater program that maps the water resources and designates production zones where communities can develop supplies with less conflict over fresh water. A state water plan that counts brackish desalination as a supply strategy alongside conservation and reuse, with state funding behind it. And groundwater management by local districts that regulate production and require monitoring, so that the aquifer is managed as a resource rather than mined.
Texas also shows the concentrate problem clearly. Most Texas inland plants inject their concentrate into deep saline formations, some use evaporation ponds, and a few discharge under permit. The Texas Commission on Environmental Quality permits the injection wells and the ponds, and the permitting of the concentrate route is routinely the longest item on a Texas project schedule. State-funded research on concentrate management and brine management, including at the federal groundwater desalination research facility in New Mexico that Texas utilities use, is where much of the practical knowledge on inland brine has come from.
For a Texas community or industrial site, the path is well worn: confirm the saline resource using the TWDB’s mapping, model the aquifer, choose the concentrate route, and take the project to the state and the local district with all three in hand. The same path works anywhere the resource is being developed for the first time.
How brackish water desalination works
The process is reverse osmosis, and the systems are the same technology used on the coast, run at lower pressure.
Wells bring the groundwater to the surface and the treatment begins there. Because the aquifer has already filtered it, treatment ahead of the membranes is usually light, the pretreatment systems are lighter, and the whole treatment train is shorter than a coastal plant’s: cartridge filtration, antiscalant dosing, and sometimes iron and manganese removal ahead of the membranes. Brackish water reverse osmosis systems, often abbreviated BWRO, then separate fresh water from the salts at 10 to 25 bar, a fraction of the 55 to 70 bar the ocean needs. Recovery is high, typically 75 to 90 percent of the feed becoming product, against 40 to 50 percent on the coast. In United States units, a system taking in one million gallons a day of brackish water delivers 750,000 to 900,000 gallons of fresh water. Post-treatment stabilizes the water and, for drinking supplies, disinfects it to drinking water quality. Treatment overall is simpler, and the plants show it.
The concentrate, 10 to 25 percent of the feed, carries all of the salt at four to ten times the original concentration. That is the stream that decides the project.
| Feature | Brackish water reverse osmosis (BWRO) | Seawater reverse osmosis |
|---|---|---|
| Feed salinity | 1,000 to 10,000 milligrams per liter | 35,000 and up |
| Operating pressure | 10 to 25 bar | 55 to 70 bar |
| Recovery | 75 to 90 percent | 40 to 50 percent |
| Energy per cubic meter | Low, often under 1.5 kilowatt-hours | 3 to 4 kilowatt-hours |
| Pretreatment | Light; well water is pre-filtered | Heavy for open intakes |
| Brine volume | Small | Roughly equal to product |
| Brine disposal | Hard; no sea | Outfall available |
| Main risk | Aquifer salinity rising over time; concentrate route | Intake ecology; discharge limits |
Why BWRO is growing
Three pressures push inland communities and industries toward saline groundwater supplies. The applications range from municipal supply to industrial process water.
Fresh groundwater supplies are running out. Over-pumped aquifers are dropping and, near coasts, turning saline, and communities that relied on them need other supplies. The saline layers below or beside them are often vast and untouched.
Surface water supplies are committed. Rivers and reservoirs in dry regions are fully allocated, and new water rights are unavailable at any price.
Reverse osmosis systems and membranes have become cheap and modular, and packaged solutions are available off the shelf for most applications. An inland system serving a small community or an industrial site is a containerized package, not a construction program, and the energy per cubic meter is a fraction of the coastal figure.
State programs now support these applications. Texas has a groundwater program that maps the state’s saline resources and designates production zones; the federal Bureau of Reclamation runs a national groundwater desalination research facility in New Mexico. Both exist because the water resources are large and the demand from communities is real, and both have produced research that a new project can draw on rather than repeat.
The concentrate problem
Everything easy about BWRO is undone by the brine if it is not planned for.
Inland, the options are deep well injection into a saline formation below the drinking water aquifers; evaporation ponds where land is cheap and the climate is dry; discharge to a sewer or a surface water where the volume is small and the permit allows; blending into a larger, lower-quality stream; or concentration toward zero liquid discharge, which is expensive but sometimes the only route. Each has a permit and a cost, and the permit is usually the schedule.
The concentrate is also concentrated. Whatever was in the groundwater, arsenic, boron, radium, or selenium in some aquifers, is now four to ten times stronger, and the disposal permit will look at concentration, not only volume. An inland system whose feed quality is safe can produce a concentrate that is regulated as a hazardous waste. The water analysis, again, is what tells you in advance.
We compare the routes in our guide to brine disposal methods, and the pond option specifically in our guide to evaporation ponds.
Pushing recovery higher
Because inland brine is expensive to dispose of, BWRO plants push recovery as high as the chemistry allows. Every percentage point of recovery is less concentrate to inject, evaporate, or haul.
The limit is scaling. Calcium sulfate, calcium carbonate, silica, and barium sulfate come out of solution as the concentrate strengthens and foul the membranes. Antiscalant dosing, softening between stages, careful membrane staging, and advanced membranes built for concentrate duty push recovery from a conventional 75 percent toward 90 and beyond, high enough to shrink the concentrate. Advanced treatment of this kind costs more up front and saves on the concentrate for the life of the system. Some systems add advanced concentrate solutions: a second set of membranes or an electrodialysis step, to squeeze the brine further. The trade is more equipment, more chemicals, and more energy against a smaller disposal problem, and it is a calculation we run on every BWRO project.
On large brine streams the same logic carries all the way to salt recovery. Our project in Indonesia is designed to concentrate a coastal desalination reject stream of tens of thousands of cubic meters a day into salt and chemicals rather than disposing of it. Few inland plants are that large, but the principle applies: the less you throw away, the smaller the permit problem.
The aquifer over time
A coastal system’s feed is the same every year. An inland system’s feed is not.
Pumping a saline aquifer changes it. Salinity can rise as fresher water is drawn down and saltier water moves in. Water levels fall. Neighboring wells feel it. A system designed for the water in the first well test can find itself treating water half again as salty a decade later, with membranes, pressure, and recovery all sized for the wrong feed.
Good BWRO projects therefore begin with hydrogeology: test wells, pump tests, and a groundwater model that predicts salinity and drawdown over the plant’s life. The design allows for the water in year twenty, not year one, and the permit application shows the regulator that the aquifer has been thought about. In Texas and several other states, saline groundwater production is regulated by groundwater management districts that will ask for exactly that, and good groundwater management is what keeps the supply reliable.
Permitting a brackish desalination system
An inland desalination system touches four sets of approvals.
Groundwater production. Well permits and, where a groundwater district or state agency manages the aquifer, a production permit with limits and monitoring. Designated production zones in some states simplify this.
Drinking water, if the supply is municipal. State drinking water approval of the treatment process, the treatment systems themselves, the product water quality, and the operators.
Concentrate disposal. An injection well permit under the Underground Injection Control program, a pond permit as a no-discharge wastewater facility, or a discharge permit, depending on the route. This is usually the longest lead item.
Construction and land. The usual local approvals, plus power connection.
We map all four, with the agencies, the studies, and the order, before the plant is designed. On these projects the concentrate permit and the groundwater model usually set the schedule, and both should start before the equipment is ordered.
What brackish desalination costs
On energy and equipment, BWRO is cheap for most applications. Pressure is low, recovery is high, treatment ahead of the membranes is light, and the plants are modular. Energy per cubic meter can be a third of the coastal figure or less, and capital per cubic meter per day is well below.
On brine, it is expensive. An injection well is a capital project. A pond needs land and a liner. Hauling costs per load forever. In some inland projects the concentrate route costs more than the treatment systems.
On the aquifer, it has a cost coastal desalination does not: the hydrogeology, the monitoring, and the risk that the feed changes. Resource management is part of the system’s cost, and regulators treat aquifer resources as shared resources with a management plan behind them. We cover the full cost structure in our guide to desalination plant costs.
Mistakes we see on inland desalination projects
Designing on one well test. The aquifer changed and the membranes were sized for the wrong water.
Assuming the concentrate can go to the sewer. The treatment works refused, or the concentrate exceeded the metals limit.
Ignoring the trace contaminants. Arsenic or radium that was fine in the feed made the concentrate hazardous.
Chasing recovery without softening. The membranes scaled at 80 percent and never reached the design figure.
Permitting the system before the brine. The system was built, the injection well was denied, and the system sat idle.
Frequently asked questions
Is brackish water desalination cheaper than seawater desalination?
On energy and equipment, yes, often by half or more, across most applications. On concentrate disposal, usually no, because there is no sea. The total depends on the brine route and on the aquifer.
How much water does a BWRO system recover?
Typically 75 to 90 percent of the feed becomes fresh water, and some systems go higher with concentrate staging on the membranes. Coastal plants recover 40 to 50 percent.
What happens to the salt from BWRO?
It leaves in the concentrate, at 100,000 to 250,000 gallons for every million gallons of feed, which is injected into a deep saline formation, evaporated in a lined pond, discharged under permit where the volume is small, or, on large streams, concentrated to recover the salt.
Can a saline aquifer run out?
The aquifers are large, but they are not infinite and they change as they are pumped. Water management and groundwater management matter, and both are now part of the permit. Salinity can rise and levels can fall. A groundwater model and monitoring are part of any responsible inland desalination project, and regulators increasingly require them as part of aquifer management.
In short
Brackish water desalination is the cheapest new water supply most inland regions and communities can get, and the concentrate is the hard part. Treat the aquifer as a managed resource, not a mine. Analyze the water, model the aquifer, plan the brine route and the concentrate solutions with the system, and permit the concentrate before you order the membranes. The energy and the equipment will take care of themselves.
If you are sitting on a saline aquifer and want to know what it would take to use it, send us the water analysis and the site. Call (470) 714-8564 or request a consultation. Our desalination page explains the full process, and our guide to the environmental impact of desalination covers what the regulator will ask about the aquifer and the brine.
Talk to us about your desalination project
Send us your water analysis, the volume you need, and the site, and we will tell you what system fits, what it takes to permit, and how long it will take.