The city of 330,000 people placed 4th in this year’s competition. It was No. 3 in 2011. Santa Ana gets more than 60 percent of its water supply from its own groundwater wells, and buys the rest from the Metropolitan Water District of Southern California. “The groundwater is pretty much ready to drink as soon as it is pumped,” a local official says. “The only treatment the city does is add a tiny (0.4 parts per million) amount of chlorine to protect against contamination.”