Howdy roadrat57, I doubt there is an average as everyone is different (to include one's equipment). In conservation mode, I can get by four weeks on 115 gallons. Normal-ish use and it lasts about 3 weeks. However; it is only me and I have learned how to conserve.
An adult male is supposed to drink almost a gallon of water per day. I make about 1/2 gallon of coffee/day, more in the colder months. I've never made an effort to measure the water used in a toilet flush but suspect it is something around a cup for a small job to much more for the bigger jobs.