Peer pressure can do a lot of things -- influence the clothes you buy, the cars you drive, even the friends you keep.
And now drought-stricken water suppliers are discovering peer pressure is an excellent water saving tool.
In the first large test program of its kind, 10,000 East Bay households cut water use by 5 percent over a year after getting regular reports comparing their use with similar size homes in their neighborhood.
East Bay Municipal Utility District households using less than the average for like homes got their water use reports stamped with a smiley face.
Households with average use got neutral faces. Households using more than the average got a stern face on their report, along with Web links to conservation tips tailored to their household.
The district board will be asked later this month to expand the program, which compares customer use to a neighborhood norm based on similar sized houses, families and yards.
"We get asked all the time by people who believe they use water efficiently, 'What is a standard?'" said Richard Harris, EBMUD's manager of water conservation. "This water report provides a goal tailored to similar households, and information how to reach it."
Psychologists say the comparison approach makes use of social norm based efficiency standards, which have been used to reduce natural gas and electricity use but not water use.
It's based on a common human desire not to be too different from the pack, said Wesley Schultz, a psychology professor at Cal State San Marcos.
"Absolutely, there is peer pressure involved here," said Schultz, who has studied social norms as a conservation tool, although he was not involved with the EBMUD test. "We don't want to be too different, so people who use more than their neighbors are motivated to save."
Water use can vary widely from home to home with differences in climate, home and family size, and landscaping. An average EBMUD home uses 250 gallons a day, but use is less in cooler areas with smaller yards and higher in hotter areas with bigger yards.
But wherever people live, surveys show most customers underestimate their water consumption, which is typically listed as gallons per day on water bills, said EBMUD spokeswoman Andrea Pook.
"The water bill isn't a great benchmark," Pook said.
But the household comparison reports can help save in the short term during droughts and in the long term to manage demand, said the California Water Foundation, a nonprofit research group that co-sponsored the test.
The household reports were designed by the WaterSmart Software company and sent out every two months from June 2012 to June 2013.
Most customers picked for the test were from Castro Valley because of the area's mild weather and modest-size homes.
Jim Robson, of Castro Valley, took part. He said seeing the water comparisons provided a wake-up call that made him decide to tear out his lawn last fall and plan to switch to low water use landscaping and irrigation.
"I try to be green, but I was surprised we were using as much water as we were," Robson said. "The reports helped to frame things."
Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff.