In a development that casts significant doubt on whether Silicon Valley’s largest water district will help pay for Gov. Jerry Brown’s $17 billion Delta tunnels plan, a majority of Santa Clara Valley Water District board members now say they want to put the issue to a public vote.

The district, which provides 1.9 million residents of Santa Clara County drinking water and flood protection, has been a key player in Brown’s controversial plan. Its share of the tunnels project could cost up to $1.2 billion.