Under Pressure: Startup Company Turns Water into Power

When Frank Zammataro thinks about water pressure, he sees an opportunity to create electricity. Zammataro, 53, is President and Co-Founder of Rentricity—a New York City energy company that has discovered a new way to tap into the excess pressure in water-treatment plants, reservoirs, and factories to help power our water infrastructure, which consumes four percent of America’s electricity.


Rentricity was born when Zammataro’s prior company was displaced in the chaos following the terrorist attacks of 9/11. Overnight, his office at 150 Broadway—two blocks from the World Trade Center—became uninhabitable.

The firm scrounged up replacement workspace in a conference room in midtown on the 40th floor. It was in that office where Zammataro noticed a neighboring water tower, the type of shingle-sided tank that is ubiquitous in New York and maintains water pressure in a tall building.

“We joked about it day after day, imagining it working every time someone uses the commode,” Zammataro said.

Upon further consideration, Zammataro, a former information-technology specialist at Merrill Lynch, started to see water pressure as a business opportunity. Could all that compression be used to spin a turbine and create electricity?

Zammataro did some digging and quickly learned that the pressure in the pipes of a skyscraper isn’t all that great. But then a professor at Rensselaer Polytechnic Institute introduced him to the pressure reduction valve, and the whole game changed.


When a massive quantity of water is transported from high elevation to low, the water builds up more pressure than its receiving station can handle, up to 150 or more pounds per square inch (psi). As a point of comparison, the pressure that supplies your morning shower—and those spectacular street gushers—is as low as 35 psi. That pressure is stepped down by a pressure reduction valve, diffusing the energy with the help of a coiled spring.

Rentricity was born when Zammataro realized he could replace the pressure reduction valve with an impeller, which runs a generator. The company figured out how to construct this relatively cheaply with off-the-shelf parts.

Rentricity’s signature project is the water treatment plant in Keene, New Hampshire. There, raw, untreated water arrives from a reservoir in the town of Roxbury, a few miles away and 90 feet higher in elevation. The water arrives at an unusable 150 psi and is reduced to 90 psi—formerly by pressure reduction valves, but now by two of Rentricity’s generators. Between them they create 62 kilowatts.

Kürt Blomquist, the Public Works Director of Keene, says the technology has cut the plant’s energy bill in half. “Generally we have generated more power than what the plant required,” he said. “The power company will be owing us money.”


The wattage they produce is tiny compared to a traditional hydroelectric dam, but still a valuable prospect for water utilities, where up to a third of operating costs go to paying the energy bill.

“I think it’s very promising and one of the best near term opportunities” for hydrokinetic power, said Peter Asmus, Energy Analyst at Pike Research. “The siting is fairly easy because they’ve already sited so much infrastructure there and in an industrial site people aren’t as concerned about aesthetics.”

Rentricity is poised to build a far larger plant, capable of producing 350 kilowatts, in Palos Verdes, California.

Zammataro sees a $5.8 billion market for equipment and a $1.8 billion market for the electricity generated worldwide at water treatment plants, industrial facilities, power plants, and mining operations—basically anywhere where there is enough of a vertical drop and sufficient water flow.

The firm is targeting cities at the base of the Appalachians and the Rockies, where elevations provide the necessary water squeeze.

One such metropolis is New York City, where more than a billion gallons of water flows through the pipes each day, pressurized in part by reservoirs upstate.

Rentricity is participating in a study to see if its generators could work at the city’s wastewater outfall pipes. If successful, Rentricity will have a unique opportunity to create clean power in the city where the whole idea began.

David Ferris is editor of the Matter Network and author of Innovate, a column in Sierra magazine about cleantech and the people who make it. He lives in Washington D.C. and should figure out how to use his compost bin any day now.

This article was originally published on Ecomagination and was republished with permission.

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