The collapse of a $1.5 billion plan to enlarge Los Vaqueros Reservoir in Contra Costa County and share the water with residents across the Bay Area is a disappointing setback for the state’s efforts to expand water storage, and should be studied to reduce the chances of it happening again with other projects, state water officials said Wednesday. At a meeting in Sacramento, several members of the California Water Commission, a state agency which had promised the project $477 million in state bond funding in 2018, said Contra Costa Water District leaders should have kept them better informed when negotiations between Bay Area water agencies on costs and risks began to unravel this summer. …  The project was scheduled to begin construction by next year. It was considered by water experts statewide as one of the most promising ways to expand California’s water supplies in an era of more severe droughts. It had no major lawsuits and wasn’t controversial with environmental groups, largely because it was proposing to expand an existing reservoir rather than damming a river.