Turning saltwater into drinking water: A breakthrough in desalination tech

Indian researchers have developed a new siphon-based thermal desalination system that can now transform salty seawater into clean drinking water faster, cheaper and more reliably than existing methods.

This could help secure safe drinking water for millions in water-stressed regions. From small villages to island nations, the siphon-powered desalination system may finally make the ocean a dependable source of fresh drinking water, according to information shared by the Ministry of Science and Technology.

Traditional solar stills, which mimic nature’s water cycle, have long been promoted as simple water purifiers. However, they face two persistent challenges - salt buildup where crusts form on evaporator surfaces, blocking water flow, and scaling limits as wicking materials can only lift water about 10–15 cm, restricting system size and output.

A team from the Indian Institute of Science addressed the challenges using a deceptively simple principle of siphonage, a phenomenon where liquid flows through a conduit from a higher elevation to a lower one due to pressure difference created by gravity. “Finding solutions to alleviate salt accumulation and boost water productivity rate is of immediate importance for the passively operated thermal desalination systems," the researchers said.

At the heart of their system is a composite siphon - a fabric wick paired with a grooved metallic surface. The fabric draws salty water from a reservoir, while gravity ensures a smooth and continuous flow. Instead of allowing salt to crystallixe, the siphon flushes it away before build-up occurs.

The water spreads as a thin film across the heated metal surface, evaporates, and then condenses just two millimeters away onto a cooler surface. This ultra-narrow air gap significantly enhances efficiency, producing more than six liters of clean water per square meter per hour under sunlight — several times higher than conventional solar stills. By stacking multiple evaporator–condenser pairs, the device recycles heat repeatedly, squeezing maximum output from each ray of sunshine.

“The ability of the desalination system to maintain a high-water productivity flux even when the evaporator area is increased by four times demonstrates its scalability to achieve higher desalinated water productivity rate,” the researchers said.

The desalination unit is low-cost, scalable and sustainable, relying only on simple materials such as aluminum and fabric. It can run on solar energy or waste heat, making it suitable for off-grid communities, disaster zones, and arid coastal regions. Notably, it can also handle extremely salty water having up to 20 per cent salt, without clogging, which is a major advance in brine treatment.

“Recent advances in thermal localisation-based passive solar desalination provide a great opportunity for the economical generation of freshwater, particularly in regions with insufficient energy and water infrastructure,” the researchers said. Their work, supported by the Department of Science and Technology, has been published in Desalination, a Netherlands-based peer reviewed journal.