Since 32% of all of American water use is irrigation, I'd probably start with improvements and moves towards more drip irrigation. For domestic use, toilets see

Since 32% of all of American water use is irrigation, I'd probably start with improvements and moves towards more drip irrigation. For domestic use, toilets seem to represent ~24% of use, so moving to dual flush toilets could probably make a big dent. Outdoor water use for homes contribute between 30% and 60% depending on region so discouraging green laws in arid regions is probably a good idea, and that seems to be happening.