San Diego roofs and streets are rainwater collection devices, and currently most of that water is drained away rather than stored for later use. That need not be. By improving the design of our streets, houses, lives, etc--we'd probably not need desal or piped water from NorCal.
Back in September Brad Lancaster gave a presentation on rainwater harvesting right here in San Diego!
I encourage you to share your own photos here about how San Diego or Tijuana urban design could be improved. Ask me how.