Steve - True, but a LOT less expensive than building houses w/o any water. A new subdivision was approved here in my county.. and there's only like 0.40 acre-foot of water per house.. and they want to build 12,000 houses!! Water's in pretty short supply here in the Denver metro.. it all ends up going downriver to NV/AZ to water their lawns. LOL. (just pickin' on ya).
And the eastern flatlands of CO don't need it.. they get 5 times the rain we do.
But I *LOVE* how you actually thought about it & broke it down.. very scientific & methodical! And STILL cheaper than spending $$ on wars that the US populace doesn't want. Not to mention how the price of flood insurance would go down & how many people's lives would be made easier in the midwest/Atlantic states if we were able to harvest those flood waters that seem to hit that area often.. even the hurricanes that hit the gulf coast could be harvested. We could make Death Valley into another Lake Mead.
