Water & Drought

Do automatic-flush toilets waste or save water?

Q: Most times when I use an automatic-flush toilet in a commercial building, it flushes two to three times. Do automatic-flush toilets waste or save water? – Ed Zajac, Orangevale

A: Your experience is common and it seems these devices do not save water, according to several studies, and may actually use significantly more than old-school manual valves.

John Koeller, a Yorba Linda-based engineer and water efficiency expert, said the primary benefit of automatic- or sensor-flush plumbing fixtures is improved hygiene, not water savings. Koeller is a partner in an organization called MaP Testing, which for years has conducted independent testing of various plumbing fixtures.

In 2010, Koeller and a colleague studied sensor-flush toilets in the real setting of a Florida office building. After months of monitoring, they found that sensor-flush toilets actually increased water consumption by 45 percent compared to manual-flush toilets. The cause was so-called “phantom flushing,” or multiple false flushes produced by over-active motion sensors on the toilets.

“It’s a big problem. It’s a problem also with urinals,” said Koeller. “A lot of manufacturers do not like these studies to be out there. Water-efficiency people like myself, they don’t recommend sensor-flush valves.”

The problem is that most toilet motion sensors point out into the room or the stall, where there can be lots of motion. He said one manufacturer, Kohler, makes a motion sensor that avoids this problem. The sensor points straight up, and the user must wave his or her hand above the sensor to flush the toilet.

Water waste also can occur with automatic faucets, but for a different reason. With a manual faucet, the user rarely turns the water on full-blast. But the automatic faucet always opens wide, causing maximum water flow for the entire duration that it’s in use. This problem may abate, however, as building owners gradually upgrade fixtures. New faucets are restricted to a maximum flow of a half-gallon per minute, Koeller said, which is about equal to the setting most people prefer when they can turn the water on for themselves.