Many areas of the country are experiencing drought conditions. Even if your area isn't, is it ever a bad idea to try to live in a more sustainable manner?
A rain barrel is an easy way to start. You'll have plenty of water for your garden and lawn, and could even use the water to wash your car, dog, etc. (though it is not suitable for drinking!) There are simple instructions on how to build one at
http://www.epa.gov/region3/p2/make-rainbarrel.pdfor plenty of places to buy one:
http://rainbarrelguide.com/