The 4 gallon toilet you mention has not been used for many years. Any modern toilet uses 1.6 gallons per flush.
Let's not forget the water does not disappear we still have the exact same amount as ever!
I have a LARGE RV and LARGE truck to pull it with. I also have a LARGE house and LARGE shop to house my fuel consuming toys. I apologize for nothing!
I do have a Motorcycle now, it's NOT to save fuel it's for fun.
There is a huge amount of natural gas and oil under the soil in this Country that has no visible end. As time goes on there will be other methods created to power our lifestyles.
Oh yea you plug in people that think they are zero emissions, what about the impact on the "Environment" just producing the vehicle? Oh yea let's not forget when plugging in you are either using power generated from Natural gas, EVIL Coal, Killing Salmon with Hydro or OMG Nuclear power!!! There is a minute amount of power generated from wind and solar but they also consume natural resources to manufacture. Problem wind mills kill birds and solar is only good for a few years. The last two mentioned only produce a spec of the total power produced in this country. They are mostly feel good resources.
Use what you want and need just don't be wasteful.