Where I live, the sewer charges for the year are based off of your water usage during the coolest, wettest months of the year in winter. My water usage (3 person household) is about 80% higher in the 3 hottest summer months. The rest of the year, there is no need to water anything unless you planted a completely inappropriate landscape or you enjoy seeing your money runoff into the storm sewers.
I pulled my figures for the past year. We used approx 36,000 gallons in household use and 9,000 gallons in irrigation/outdoors use. Effectively, my lawn is equivalent to one additional person living in our home.
It's tricky in a transitional zone. One week of extreme heat and dry weather can erase a lawn that survived a decade. For ~7500 sqft of lawn, you can get by with about 1500 gallons for each of three days and have a good chance of surviving that event.
I find that most of the time, it's not the heat or dry that's killing lawns, it's disease and pests. If I was foolish enough to water fescue regularly in the summer heat, I would lose it to dollar spot or brown patch. I've been completely wrecked by web worm while on vacation. I have a new residence with a larger lot and plan to switch away from fescue once I've lived here a few seasons. I'm also convinced the USDA 2012 hardiness zone map is overdue for an update. Regardless, I'm not going back to a high maintenance lawn.
I pulled my figures for the past year. We used approx 36,000 gallons in household use and 9,000 gallons in irrigation/outdoors use. Effectively, my lawn is equivalent to one additional person living in our home.