OAKLAND -- The East Bay's largest water supplier failed to give the public an adequate explanation of a 9.75 percent water increase, the first of two big increases in consecutive years, Alameda County's civil grand jury has concluded.

The panel of government watchdogs said they lacked the expertise to second-guess the need for the increase. But jurors said the East Bay Municipal Utility District, which provides water for 1.3 million people in Alameda and Contra Costa counties, wasn't clear in explaining the need for the increase and its impact.

In a report released this week, the grand jury also said the water board rate decision wasn't very accessible to the public because the meeting was held on a weekday afternoon and neither broadcast nor webcast.

"The grand jury has found that EBMUD has not been sufficiently transparent in its efforts to justify the recent rate increase to the public," jurors wrote.

District spokeswoman Abby Figueroa said Wednesday her water agency is considering ways to improve communications about future increases, including another large one expected next year. "Their criticism is being heard," she said.

Jurors said the district publicly understated the impact of the increase by relying on average consumption for residential users and not spelling out the effect on bigger water users -- often found in inland areas with larger yards.

Jurors also suggested the district consider showing its meetings on the Web or on public access TV stations, or hold night meetings.

Few people typically attend water board meetings, yet the water board can get more money from the public by a simple water board vote, unlike cities, counties and school districts that must go to the ballot.

EBMUD officials say they tried night meetings previously, but few people came.

The water district said the rate increases were essential to do pipe repairs and other improvements postponed during economic hard times.

Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff