Collecting rain water is an ingenious way to conserve water and keep your lawn watered during a drought.  Garden centers sell "rain barrels" which is used to collect storm water from downspouts. Depending on the size of your lawn, you may need several barrels to adequately water your lawn. It takes approximately 52 gallons to apply 1 inch of water to 1,000 square feet or 2,260 gallons per acre. 

You can also hav underground water storage systems installed. This allows you to pump water up to the surface to keep your lawn green. After the initial cost and install, these systems can be financially beneficial in high water cost or water restricting areas.