Panic over saltwater intrusion in the Mississippi River threatening drinking water supplies in major cities and an ongoing drought parching the West have some officials weighing a controversial solution — desalination.
But the process of removing salt from water to make it potable comes with a variety of drawbacks that complicate widespread viability.
“It is costly to build and operate desalination plants,” said Mary Grant, a campaign director with the group Food & Water Watch, who added that while the practice has been “a hot topic” in drought-ridden states like California, “its main hurdles have been cost and environmental impacts.”
Countries like Saudi Arabia, Israel and the United Arab Emirates all operate desalination plants that help provide drinking water. In the U.S., plants are scattered across states with saltwater intrusion problems and drought concerns, namely in Florida, California and Texas.
It is unclear how many facilities are currently operational, but a 2018 report from the U.S. Bureau of Reclamation found there were more than 400, with around half those being operational.
Reclamation noted via email that it does not compile data on who relies on desalinated water, as that varies “from individual water supplier to water supplier.”
Desalinated water typically makes up only a portion of a water supply’s portfolio, even in places like San Diego County, Calif., home to the biggest plant in the country. Another large facility, Tampa Bay Seawater Desalination, provides up to 25 million gallons per day of drinking water for a region of more than 2.5 million people — but similarly supplies only up to 10 percent of the area’s needs.
Despite the limited benefits to water supply needs, new or exacerbated environmental challenges have helped bring desalination under broader consideration elsewhere.
For example, drought impacting the Mississippi River coupled with a long history of dredging by the Army Corps of Engineers has helped drive saltwater intrusion for the second year in a row, threatening drinking water in populous cities like New Orleans.
Grace Birch, a spokesperson with the Sewerage and Water Board of New Orleans, said that the city is “confident that long-term solutions can be accomplished” at a reasonable cost and with input from state and federal holders.
How? Sewerage and Water Board of New Orleans officials have pointed to desalination as a significant option on the table.
But even as New Orleans and other areas explore desalination, obstacles remain, and those drawbacks could make it hard to scale the practice nationally.
1. Energy and water use concerns
Desalination facilities suck up significant energy to run.
The Intergovernmental Panel on Climate Change has pointed to that reality as a reason why desalination is “maladaptive.”
Some advancements have helped make the process less energy-intensive, but opponents say that won’t solve the scope of the problem. Most plants consume tons of electricity while emitting carbon dioxide, sometimes hitting the equivalent of 52,000 cars driven annually.
What’s more, water intake can also disturb wildlife and its broader environment.
On the other end of the spectrum, facilities discharge brine — the salty byproduct of the desalination process. Brine often contains contaminants like chlorine and copper, which then reenter the ocean when released by facilities.
Desalination typically results in 1.5 liters of brine to every liter of potable water, making it a massive quandary for facilities. When pumped into the ocean, brine can cause ocean acidification, which can harm shellfish and ultimately people, in addition to bringing higher temperatures.
Grant noted that desalination typically involves either ocean or brackish water. That second type has more saline than fresh water but not as much as a marine environment, and is a more common focus in the United States.
"Brackish desalination, because it’s non-coastal, typically has brine disposal challenges," she said.
That could be a problem for southeast Louisiana.
"Ocean desalination plants typically dump into the ocean," Grant continued. "If this brine on the Mississippi is dumped back into the Mississippi, it could harm ecosystems and worsen the water quality."
2. Cost concerns
Another looming obstacle for desalination proponents is its price tag.
Ocean desalination in particular is the most expensive source of potable water. While it provides consistent water unimpeded by drought, the largest U.S. desalination plant — the Carlsbad facility in San Diego County — produces water that costs around $2,725 per acre-foot, or approximately 326,000 gallons. That is enough to serve 400,000 people, according to the San Diego County Water Authority. But it accounts for only about a tenth of the current supply for the county, which draws its water mostly from other sources like the Colorado River.
Desalinating brackish water is also expensive. The New Orleans water board has acknowledged that building a plant would require federal assistance, as well as major coordination among utilities.
"There’s no parish in this region that can afford to pay for construction of a new desalination plant," said Ron Spooner, the Sewerage and Water Board of New Orleans interim general superintendent, while speaking with New Orleans City Council members earlier this month.
Birch, the board spokesperson, told E&E News that "it would be premature to speculate on the specific technologies or cost" associated with solutions to saltwater intrusion but that officials expect to be able to keep costs in check.
Still, critics worry that expenses could be passed on to ratepayers, exacerbating environmental justice issues. Low-income communities of color disproportionately struggle with water bills, especially in cities like New Orleans.
"When households cannot afford their water bills, they face the threat of shut-off, losing running water necessary for hydration and sanitation, and many related harms," said Grant.
Proponents counter that investing in desalination now will save money down the line. Salt can corrode service lines, leading to health issues and additional water costs. And investments could possibly go beyond weeding out salt.
Desalination technologies vary, but many facilities rely on a membrane process called reverse osmosis, which strains salt from water. Such a filter could have additional benefits: Reverse osmosis is one of the primary means of filtering out PFAS (per- and polyfluoroalkyl substances), for example, some of which are set for EPA regulation and likely to become a major issue for utilities.
Even without those co-benefits, New Orleans officials have been blunt that desalination might also be the only path forward if the region wants a fix for its saltwater problems in the years to come.
"You’re pretty much down to desalination in order to effectively have a long-term solution," said Spooner.
3. Pushback and alternatives
While cost and the need for vastly expanded infrastructure are most likely to deter officials from desalination, they also face pressure to weigh other options.
In the West, experts have voiced skepticism around investing heavily in technology without first exhausting other alternatives, like ensuring proper water conservation practices and reining in industries that burn through water like agriculture.
Other sources of water loss include aging and outdated pipe systems, which leak and contain contaminants like lead. Groups like Food & Water Watch maintain that updating those service lines and embracing "green infrastructure" while also adopting water conservation practices will naturally ease water demands in regions like the West.
In southeast Louisiana, meanwhile, the current crisis in the Mississippi River has been exacerbated by dredging activities in the name of expanding shipping and trade. Supplementing river flows from upstream reservoirs can help offset some of those impacts and has become increasingly common for Corps projects in the Mississippi basin.
A major factor in slowing this year's saltwater wedge has also been the construction of an underwater barricade, or sill. Cullen Jones, commander and engineer for the Army Corps' New Orleans District, called that an "additional speed bump'' that worked in concert with other factors to buy the city a reprieve. The success of that sill might be replicated if a similar problem crops up.
Beyond those alternative measures, desalination opponents are also worried about implications for vulnerable communities. Projects in states like Texas have faced major pushback, with residents arguing that they will benefit industry facilities that require a lot of water, rather than nearby communities.
"Desalination projects can have significant environmental justice impacts," said Grant, "with lower-income communities and communities of color shouldering the burdens while the benefits go toward wealthier, whiter residents."