Politicians, like most of the public, prefer to believe they have power over markets, and will use top-down rationing, rather than market-based pricing. See the gas/oil shortages of the 1970's, vs letting the market choose the price and having supply/demand automatically equalize based on price.

Also, some of the officials making the rules on water restrictions are guzzlers themselves [1].

1. http://www.nbcsandiego.com/news/california/California-Water-...