Not only is California in the middle of a severe drought, but clean water is a scarce resource worldwide.
We want to influence behavior change for responsible water usage via various mechanisms - quantified data (providing real-time feedback on water consumption), peer influence via social networks, and gamification.
For example, you would be alerted to your how long you were in the shower today, and how many gallons of water were used as compared to the previous day(s). You could enable sharing of this data with your circle of friends, and compete with each other. You could also challenge your friends (a la the Ice Bucket Challenge) to consume less (or as much) water as you did.