Reverse osmosis

Practical reverse osmosis emerged from a UCLA laboratory in 1959, when Sidney Loeb and Srinivasa Sourirajan created the first asymmetric cellulose acetate membrane capable of rejecting salt while passing fresh water at realistic pressures. Their invention transformed desalination from a theoretical possibility into a commercial reality, eventually providing drinking water to hundreds of millions of people in water-scarce regions.

The basic physics of osmosis had been understood since the 18th century: water naturally flows through semipermeable membranes from lower to higher salt concentrations, seeking equilibrium. Reversing this process—applying pressure to force water through membranes from high to low concentration—was theoretically straightforward but practically impossible. Early membranes couldn't reject enough salt or pass enough water. The concept seemed permanently stuck as a laboratory curiosity.

The adjacent possible opened through public interest in desalination following World War II. Fresh water was becoming scarce in California and other arid regions, and federal funding flowed to university research programs. At UCLA, Professors Joseph McCutchan and Samuel Yuster led a team exploring membrane approaches. In the summer of 1958, Sidney Loeb—a 41-year-old Jewish scientist who had worked in industry—joined the group.

Loeb and Sourirajan's breakthrough was the asymmetric membrane structure. Previous membranes were uniformly dense, requiring enormous pressure to force water through. Their new design had a thin, dense layer for salt rejection backed by a porous support layer that allowed water to flow freely. Using cellulose acetate, acetone, water, and magnesium perchlorate as raw materials, they created membranes that worked at practical pressures and flow rates.

The pair filed for a patent in 1960. The first real-world test came in 1965 at Coalinga, California—a town whose water had become unpotable due to extreme mineral content, forcing residents to receive drinking water deliveries by train. The UCLA membrane successfully purified Coalinga's water, and the world's first commercial reverse osmosis plant began operation with help from McCutchan and Loeb.

The demonstration at Coalinga drew attention from engineers and governments worldwide. The technology spread rapidly to the Middle East, where countries like Saudi Arabia and the UAE built massive desalination plants. Israel became a leader in RO technology and eventually derived most of its domestic water from desalination. Singapore, facing water security challenges, implemented large-scale RO systems.

Throughout the duration of his patent, Loeb received just $14,000 for an invention that created a multi-billion dollar industry. By 2024, approximately 65% of the world's desalination operations used reverse osmosis membranes. The technology had expanded beyond seawater to treat industrial wastewater, purify pharmaceuticals, and provide point-of-use water filtration in homes.

Reverse osmosis exemplifies how patient academic research, supported by public funding and responding to real-world scarcity, can create transformative infrastructure. Loeb and Sourirajan didn't invent the concept—they engineered the membrane structure that made it practical. Their asymmetric design remains the foundation of modern desalination.