NanoH2O, a start-up developing membranes for water desalination, said in a regulatory filing that it has raised more than $14.8 million as part of a $30.6 million fundraising effort.

The El Segundo company, specializing in reverse osmosis technology based on UCLA research in nanotechnology, already has venture funding from Khosla Ventures, Oak Investment Partners, Rusheen Capital Partners, and PCG Energy and Technology Fund. The company was co-founded in 2005 by Chief Executive Jeffrey Green and Chief Scientific Officer Bob Burk.

Investors in this latest round were not identified in the Thursday filing with the U.S. Securities and Exchange Commission.

NanoH2O’s said its thin-film membranes improve desalination energy efficiency and productivity. The technology has received several industry awards, most recently last month when it won the 2011 Aquatech Innovation Award in the “water supply” category.