I think a better more accurate estimate could be inferred thru water needs when backpacking.
In my experience backpacking when you must provide water for all your needs including re-hydrating food then 3 gal per day minimum is a better estimate,and this only allows for minimal clean-up. My wife sends me straight to the shower when I get home.
The military allows something like 5 gal per day when you are working in a hot dry environment.