Something to keep in mind here is that water consumption by humans is dwarfed by most agricultural and industrial uses. This is why one of my guiding principles of human settlement, land development and civil engineering is that water resources should be used as a rigid determinant of where many land uses should be permitted. If an area doesn't provide enough rainfall to support more than X people, Y head of cattle, or Z acres of orange groves, then it probably isn't a good idea to plan and design around values that exceed X, Y and Z in this case.
There's always room to use conservation, creativity and technology to push the limits on X, Y and Z -- but I would much rather see these as interim measures or stop-gap measures for unusual conditions.