Denver has hit turbulence in its biggest water-supply project since the 1960s — a $225 million effort to prevent future shortages. Denver Water proposes to divert enough for 45,000 families from mountain rivers on the western side of the Continental Divide, then pump it through tunnels to Front Range reservoirs, including an expanded Gross Reservoir above Boulder. But the plan requires federal approval, and at public hearings, opponents concerned about environmental harm have argued that Denver must rely more on using less water — not pump more from the mountains.