Average water use per shower?

I have a 34 gallon FW tank. Navy showers every other day, using the toilet and using bottled water for cooking and coffee i can go 8 days on about 30 gallons of water. This is taking into account the water heater and system are already filled before the tank is topped off and I am traveling alone. So I guess about 6-1/2 to 7 gallons per shower.

When tent camping and using a 5 gallon solar shower bag I can get by with about 2-1/2 gallons per shower.