A 1,000 sq. ft. lawn (about normal) that is watered for 10 minutes a day with traditional sprinklers will use about 8,400 gallons per month.  If the lawn is replaced with a traditional ground-cover and is watered about 4 hours per week, the water use is about 2,100 gallons per month.  If the lawn is replaced with native ground-cover and watered with water efficient rotator-sprinklers for 20 minutes per week, the water use is about 200 gallons per month.