From the Huffington Post (Ryan Grenoble):

The current campaign — which gave rise to the billboards, bus signage, and installations — was launched in 2006 with a goal of 22% reduction in water use by the end of 2016. As of 2011, the campaign has reduced water use 20%. The campaign has cost an average of about $920,000 each year, for a total of $5.5 million over the past 6 years. “We serve 1.3 million people in Denver and the surrounding suburbs, and believe we have identified media vehicles and nontraditional approaches that are cost-effective, far-reaching and yield lasting impact,” said Stacy Chesney, a spokeswoman for Denver Water, told the HuffPost. “Our goal is to create a conservation culture where water is more highly utilized, where waste is frowned upon and where our citizens become ambassadors for water conservation.”

More conservation coverage here.