LAS VEGAS (AP) — The federal government isn’t going to tap the Missouri River to slake the thirst of a drought-parched Southwest, the government’s top water official said Wednesday.

But rising demand and falling supply have water managers in the arid West considering a host of other options to deal with dire projections that the Colorado River — the main water supply for a region larger than the country of France — won’t be able over the next 50 years to meet demands of a regional population now about 40 million and growing.