Flushing our feces with a valuable resource as precious as clean water seems wrong.  I thought if I used less, then maybe other life might get a little more but I couldn't find a product or kit so I developed one myself.  It reduced my water consumption by about 30% - your mileage may vary.  If California's 40 million people did the same, it would save 1,767 acre-ft per day (576,000,000 gallons) and that would go a long way to solving California's water woes.

You'll need to provide a small submersible utility pump and a rainwater tank or barrel that you can fill when it rains. Then place the sensor in your toilet tank and connect it to the controller. Connect the pump in the rain barrel to your toilet tank fill inlet.  When you flush, the sensor will signal the controller to turn on the utility/submersible pump in your rainwater tank to fill up your toilet's tank. Of course it stops pumping when the sensor reads full. You'll need a little DIY plumbing magic (or hire a plumber) to disable the old toilet water source line and provide a new source line from the pump to the toilet: all the details are in the free "How To" guide.