A recent article in Popular Mechanics suggests 6 radical solutions to water shortages in the Southwest. I guess if you are discussing strictly engineering solutions, those might be the most likely candidates. But those are ideas that have been under discussion for some time now and could hardly be considered radical. What about pricing water to reflect its true societal value? How about reallocation of water among use sectors, i.e. agricultural to municipal - which would be a natural result if water was priced sensibly and real markets existed. What about strict conservation measures? Not just reuse of existing water supplies, but e.g banning most outdoor water uses (where most water is used in arid areas) or tiered pricing structures create strong disincentives for excessive water use (as some cities such as Tucson now have in place). Now those are ideas I would call radical.
Their suggestion that removing salt cedar will increase supplies is debatable. Some recent studies (such as this) have indicated that salt cedar actually uses less water than many native tree species. I think the jury is still out on that assertion, but in any event my guess is that the possible gains from riparian modification are overblown.
Look for plenty of discussion on the topic of supply enhancement as long as drought in the Colorado River basin continues.
Speaking of which, I hope plenty of people saw the program on PBS recently about water supplies in the Southwest (called The American Southwest: Are we running dry?; it was on the local PBS station in Tucson last Thursday). It's message was slightly alarmist, but some good points were made.