From How Much More Rain Would California Need To End The Drought?:
Short answer: a whole lot.
...the winter we need to escape drought conditions ... would have 150 percent of the average rainfall, or a storm like we've been getting every three to five days through spring. That, unfortunately, isn't very likely.Additional coverage of the California drought on SFist.
Much of the US is in an historic drought. Drought leads to changes in food prices (almost always upward), increases costs of disposing of waste (due to cost of water and need for clean water when supplies diminish), and can literally make portions of the country uninhabitable without substantial efforts. Any number of Southern California and Sun Belt cities are in locations that are incapable of supporting their population without massive influxes of foreign water, including the possibility of moving water from Canada.
The idea of "water wars" is nothing new, but with increasing drought throughout the US ("from Delaware to California" is a money quote from one story) the problem of who has water and who's willing to give up water is going to get nothing but more serious and contentious.
Who owns your water supply? There's more...