Until recently, it was illegal to collect rainwater that fell on your roof. 
I like the idea of requiring solar panels. Homes today are becoming larger and more inefficient than they need to be, with high ceilings. I would like to see all new construction be required to put 10 percent of cost into solar panels and/or efficient construction. A $500k house with $50k of solar panels can be mostly self sufficient with minimal reduction of living space. Although a better solution to rooftop solar would be municipal solar facilities where panels can be optimally aimed without worry of trees. A shopping mall could be covered with solar panels, and be self sufficient and then some. Skylights and light piping can hugely reduce electricity needs. How much energy is wasted trying to heat and cool the huge tents at DIA? And more evaporative cooling instead of refrigeration. Then we'll need less fracking and fossil fuel use.