Let your grass grow to about 3 inches tall. Watering your lawn deeply about twice a week is better than watering lightly on a more frequent basis. Watering only in the early morning during the summer months can also help to save water. When choosing grass and garden plants, select plants that are drought-resistant. Creating a xeriscape garden can be fun and educational, and can save large amounts of water. Place mulch or compost around the base of your plants to trap water in the soil. Use a rain barrel to catch rain water and use that for watering your lawn and garden. If you must use a sprinkler, position it carefully so that you're not watering the street. Also, try using a soaker hose instead of a sprinkler.
Taking these steps will help to ensure that our water resources are put to good use. Saving water doesn't isn't about doing without; it's about water efficiency.
Sources:
"Water Facts." http://www.water.org/waterpartners.aspx?pgID=916
Associated Press, "U.S. worst for wasting water, survey shows." http://www.sptimes.com/2002/12/12/Worldandnation/US_worst_for_wasting_.shtml
"The World Water Crisis" http://www.worldwaterday.net/index.cfm?objectid=E39A970B-F1F6-6035-B9F75093B863ED13