Rocky Mountain water managers worried about climate-driven depletion across the Colorado River Basin are mulling a “grand bargain” that would overhaul obligations among seven southwestern states for sharing the river’s water. This reflects rising concerns that dry times could turn disastrous. An enshrined legal right of California and lower-basin states to demand more Colorado River water could imperil half of Denver’s water supply. The grand bargain concept arose from increasing anxiety in booming Colorado and the other upper-basin states — New Mexico, Utah and Wyoming — about their plight of being legally roped into sending more water downriver, even if dry winters, new population growth and development made that impossible without shutting faucets.