The Department of the Interior's WaterSMART program will save enough water for a smallish city — 400,000 people — yet it cost only $24 million. As Tina Casey reports at CleanTechnica, the program works by going for the low-hanging fruit: 54 separate programs that address everything from farm irrigation to water distribution infrastructure.
At $60 per person, the programs are way cheaper than finding an equivalent amount of water by pretty much any other means except dowsing — especially in the arid Southwest where there isn't any more water to be had. One of the grants simply helps defray the cost of converting open ditches into pipes; another helps a water district in southern California use high-tech mapping to identify places where it can conserve.
Of course, another way to incentivize water conservation would be to price water appropriately, instead of the insane system we have now, in which a hierarchy of "water rights" allows some (mostly agricultural) users to draw as much water as they ever have, and at a super-low price.
As one water expert at the National Center for Atmospheric Research told this reporter: "We don't have a water crisis in California, if you just look at it from the perspective of water use in cities. What we can't keep doing is growing alfalfa in the desert."