Solar Desalination Breakthrough Turns Seawater to Drinking Water Without Toxic Brine

Engineers have developed a solar-powered desalination system that turns seawater into drinking water without producing the toxic brine that has long been one of the technology's biggest environmental drawbacks — and that can recover valuable minerals, including lithium, in the process.

The device, built in the laboratory of Professor Chunlei Guo at the University of Rochester, relies on laser-etched "superwicking" black metal panels. Sunlight heats the textured surface, which draws up a thin film of seawater and evaporates it, leaving fresh water vapor to be collected. The same laser texturing that wicks the water also keeps the surface clean, automatically moving salt deposits away so they cannot clog the panel and choke off production.

Conventional desalination plants, which supply drinking water to coastal cities around the world, generate enormous volumes of hypersaline brine as a byproduct. That brine is typically pumped back into the ocean, where it can harm marine ecosystems, or requires costly disposal. Salt buildup also degrades equipment and drives up maintenance costs, limiting how cheaply and sustainably plants can operate.

Guo's design sidesteps both problems by exploiting the so-called coffee-ring effect — the same physics that leaves a dark ring when a drop of coffee dries. The panels channel dissolved salts toward a passive region at the edge of the surface, where they accumulate as solids and can be scraped off later. In testing, the team reported nearly 100 percent salt extraction in solid form, without reducing the panel's efficiency.

To gauge how the system would perform in the real world, the researchers tested it on water drawn from the Pacific, Atlantic and Indian Oceans. In each case the surface remained self-cleaning, producing fresh water while directing the leftover salts to the collection zone. Because those solids can be harvested rather than discarded, the approach turns a waste stream into a potential resource — including critical minerals such as lithium, which is in soaring demand for batteries.

The team, which described its method in the journal Light: Science & Applications, says the combination of passive solar operation, self-cleaning surfaces and mineral recovery could make desalination cheaper and far less environmentally damaging. If the approach scales beyond the laboratory, it could offer drought-stricken and water-stressed regions a way to tap the ocean for drinking water without trading one environmental problem for another. With water scarcity intensifying across much of the world, the researchers said cheaper and cleaner desalination could become an increasingly important source of fresh water for coastal and arid regions alike. The next step, they noted, is to scale the panels up and test how they hold up over long stretches of continuous outdoor use.