I had a city issued smart water meter at my last residence with 5-6 residents. I set a text message alert at 400 gallons per day, as that was a very unusual event that might warrant attention. I had high efficiency showers, toilets, and washers. I only ever hit it, and well exceeded it, when I did something like water the lawn a few times a year. A high watermark estimate (har har) would be 400 x 365 = 146000. I suppose two households is plausible, but I'd guess more like three to four for 326000.
Where I live, in a very wet part of ther United States, water is still too expensive for watering the lawn regularly. This is usually because the meter reading is used to assess charges for sewer as well. Those who do have irrigation systems request second meters to avoid sewer charges or even tap into the gray water supply.
The fact that decorative lawns exist at all is indicative of water not being expensive enough.
Edit: By decorative, I mean the manicured lawns that are only for aesthetics that require tons of watering and sprinkler systems, and pesticides/insecticides/fertilizers.
Where I live in the Northeast, the natural state of a patch of dirt--or for that matter a patch of gravel--will be to become a forest in most cases by way of grass, weeds, bushes, and trees.
To some degree. But there are a lot of reasons to keep some sort of buffer around the house in any case. Now (unless required by local regulation/HOA/etc.), this doesn't necessary mean a perfectly manicured Kentucky bluegrass lawn but in a lot of the country just letting nature take its course will have tall grass, bushes, and eventually trees growing right up to the foundations.
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.
Where I live, in a very wet part of ther United States, water is still too expensive for watering the lawn regularly. This is usually because the meter reading is used to assess charges for sewer as well. Those who do have irrigation systems request second meters to avoid sewer charges or even tap into the gray water supply.