Backers mourned the loss of Proposition 3 on Wednesday, the nearly $9 billion bond measure that would have modernized old dams, restored tainted watersheds and created desalination plants, among dozens of other water projects throughout the state. Prop. 3 — backed by state water agencies, farming organizations, social justice advocates and environmentalists, but not the Sierra Club — lost by 52 to 48 percent, a difference of 320,000 votes out of nearly 7 million ballots cast.