Speaking of water and gardening in Texas, I just have to put in a plug for my latest geeky endeavor. There is a technique known as Aquaponics that I am very excited about. Among other benefits, it only uses 10% of the water that traditional gardens do.
In short, you have a garden pond with fish in it, the fish poo in the water, natural bacteria converts the Ammonia into Nitrates (which plants thrive on) and the nutrient rich water is used to feed the plants. So, since this is a closed loop system the only water lost is that which evaporates out of the plants. As a nice side effect, if you choose an eatable variety of fish like Talipia, you can also add them to your harvest.
IMHO, the ultimate in urban sustainability.