LOS ANGELES, July 14 — The membranes that turn seawater into drinking water have a birthday worth noting. This year marks the anniversary of a pair of researchers at the University of California, Los Angeles handing the world the first practical reverse osmosis membrane. Sidney Loeb, an American chemical engineer born in 1917, and Srinivasa Sourirajan, born in 1923, produced their breakthrough membrane in 1959.
The technical reality is that they built directly on earlier work by Charles E. Reid and E.J.
Breton at the University of Florida, who had been probing the basic mechanisms of desalination through membranes in the 1950s. Loeb and Sourirajan’s contribution was to make the thing actually work at scale. Their cellulose acetate membrane achieved a salt rejection rate of 98 percent and a flux of 10 gallons per square foot per day.
Those numbers matter. Under the hood, that combination of high rejection and decent flow was what had eluded earlier researchers.
A membrane that rejects salt but passes water too slowly is a laboratory curiosity; one that passes water fast but lets salt through is useless. Loeb and Sourirajan found the sweet spot. ## From lab bench to Coalinga The first commercial reverse osmosis plant using their technology opened in 1965 in Coalinga, California, producing 5,000 gallons per day. Coalinga sits inland, in the dry western San Joaquin Valley, where brackish groundwater was a persistent problem.
The plant proved the concept could leave the lab. Loeb received the 1997 National Medal of Technology from President Bill Clinton. Sourirajan continued his membrane research at the National Research Council of Canada, pushing the field forward from a different continent.
The detail that matters here is that neither man stopped after the initial breakthrough; they spent decades refining the technology. ## The scale of what they started As of 2020, the global desalination industry — built on the foundation Loeb and Sourirajan laid — produces over 95 million cubic meters of water daily. That is enough to supply tens of millions of households, though the precise figure depends on per-capita consumption patterns that vary wildly by region.
The invention is considered one of the most important in water treatment history, and that assessment is hard to quarrel with. What to watch next is the continuing evolution of membrane materials. The cellulose acetate that Loeb and Sourirajan used has long since been supplemented by thin-film composite membranes, and researchers are now chasing graphene-based and biomimetic designs.
The fundamental problem, however, remains the one the two UCLA engineers solved: how to push water through a barrier while leaving salt behind. They got it right in 1959, and the rest has been engineering.
