What is the endurance goal you are aiming for with regards to not needing to refill? That will and should help determine how much water you want/need? The general rule is to plan for the desert with a 1 gallon-per-person per-day. Factor in a quick shower or two and you may be 7 gallons every 5 days per-person, and that's being somewhat conservative and assuming you're not showering every day. This accounts for ~32 oz for cooking and 96 oz for drinking. Waste not, want not. I say desert as generally speaking the summer is the extreme end and where you're likely to consume the most water - the desert part puts emphasis on that. In the winter we typically drink less. My opinion is to plan for at least 10 days without a need for a refill. If you could plan-for 15 days you're even better, but then food/beer become the limitation. YMMV.
Also, where do you plan to travel? If you're moving you're always going to be within easy striking distance of a fill up. There's becoming increasingly less reason to plan for long stretches of nothing in N. America. There's towns and gas stations all over, within reasonable distance from most roads for a fill up. Water = weight = diminished fuel consumption. Maybe not provisions, but fuel along with water isn't as scarce as we perceive. If you include a filtration system into your setup, then where you get water now becomes moot as with the right filter you now can fill from any freshwater source. I think there's a fear that we have to be able to carry everything all the time. Also, at some point your food supply will become the limiting factor.
I feel that 80 gallons exceeds any reasonable endurance goal you may be thinking about. Even with 3 people/2 people and a dog.