Professor Joseph Dellapenna kindly sent this table [pdf] summarizing the different property rights regimes -- Appropriative, Dual (appropriative & riparian), Regulated Riparianism, and Riparian -- for each of the 50 states. Although I know that rights correspond to water scarcity (riparian is more common in wet places; appropriative in dry), I'd be interested to know if the regimes match some measure of water efficiency and if regimes have changed to improve things.
This website (and this one!) provides data on per capita water consumption (perhaps indoor only?), a concept that is very important and often unmeasured. I'd LOVE to see an open access listing of per capita consumption for US cities. Anyone?
Top consumption award (as reported) goes to UAE, at 500 liters/capita/day. Canada comes in at 326 lcd, then the US at 295 lcd. According to the other site, the US leads at 575 lcd, so that's probably indoor and outdoor.
Bottom Line: Property rights can drive water use, and measurement of water use is critical to understanding how well water is managed. No rights, no management; no measurement, no management.