The system uses excess pressure in the water system to spin a Swiss-built turbine, which generates electricity to power the lights in a back room. Mr. Ng is also installing turbines in the company’s newest apartment development, The Avenue, in Hong Kong’s Wan Chai neighborhood, that should be able to power the lighting in the stairwells, elevator shafts and lobby.

There are many reasons the novel idea might not work. Small-scale systems cannot easily generate enough power to justify their cost to large developers. The price per kilowatt-hour of generating power can be five times as high as simply buying it from the grid. And factors like simple geography — will water be flowing far enough down? — can derail plans for turbines built into municipal water infrastructure.

Nonetheless, the developer has pitched the concept to the governments of Beijing, Hong Kong and Singapore. He said the feedback from Hong Kong in particular had been very positive, with the city’s new director of water supplies, Enoch Lam, expressing interest.

Hong Kong is one of the most densely populated cities in the world, with about 23,000 people per square mile in its most crowded district. About 40 percent of the city’s territory is devoted to parkland, and Hong Kong crowds people into office towers and residential apartment blocks that often top 50 stories.

“All these buildings are energy-sucking monsters,” said Claude Touikan, a Hong Kong-based director at the architecture and engineering firm Benoy, which is not involved with Mr. Ng’s project. “Of course there is potential.”