But Navarro - a controversial figure in local politics who nonetheless won both seats by commanding margins - isn't going down without a fight.
County Superintendent of Schools Gary Thomas, who is independently elected, asked for the opinion after "several" members of the public asked whether holding both positions was legal.
In a Dec. 7 letter, county counsel Jean-Rene Basle summarized published opinions from the California Attorney General's Office and concluded there was a potential conflict of interest.
The water district is in charge of long-range water supply and setting wholesale water rates for so-called retail water agencies, including the one that then decides what county schools must pay.
That could mean a conflict that's not allowed under California law, Basle said, quoting a 2002 attorney general's opinion: "A significant clash of duties and loyalties may arise in such matters as the water district setting the wholesale water rate that will be passed on to the school district by the retail water agencies involved (and) determining the need for restrictions on water usage during times of water shortage."
But no such conflict exists now, making it look like a political move, Navarro said.
"They're stretching it so thin - they're trying to substantiate their position by giving very thin examples of why it's a conflict of interest," he said. "It's just an extension of how the county superintendent of schools doesn't want me on the school board."
Navarro said he's looking for an attorney to represent him in a legal fight to keep both positions.
If Navarro won't voluntarily step down, the school board - including Navarro - will discuss the next step at its Jan. 8 meeting, said county schools spokeswoman Christine McGrew.
McGrew said Thomas wasn't available to directly counter Navarro's assertions, but there was no pressure on county lawyers to decide any particular way.
"Mr. Navarro himself chose to pursue another elected position, so that was his choice," McGrew said. "So really, this is just a matter of looking at existing law, which is pretty clear."
Navarro said he felt it was important to advocate for students and to "hold Mr. Thomas accountable" on the school board and to lower water rates through the water board.
Selective prosecution is apparent by comparing his situation to John Longville, who since 2008 has sat on both the San Bernardino Valley Water Conservation District and San Bernardino Community College District, Navarro said.
"Nobody's challenged him, but they challenge me," Navarro said. "You know why? Because nobody has a beef with John. They have a beef with Gil Navarro."
Longville said he couldn't speak to Navarro's situation, but he had researched whether his own positions involved any conflict and found none.
"I'm on a water conservation district here, which recharges the basin," he said. "We are not a water retailer. We don't sell water. And we have no relationship of any sort with the San Bernardino Community College District, nor with either of its two colleges."
Had he won his 2010 campaign for the San Bernardino City Council, Longville said, he would have resigned from the water conservation district.
This isn't the first time Navarro has ignored what he calls politically motivated legal advice.
From 2006 to 2008, Navarro was repeatedly warned by county attorneys and then-superintendent Herb Fischer of a perceived conflict between his roles as school board member and paid advocate for students struggling in school. Navarro continues both jobs, although he recuses himself from votes involving students he represents.
"They try to pin me down," Navarro said, "but people want me doing these jobs and fighting for them, and that's what I intend to do."
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