No, we can't pack 3 gallons of water. But, given a bottle of water is almost a fashion accessory carrying WHAT WE CAN is the next best strategy.

I have two old plastic military survival flasks in my sportsjackets, a few of the Mylar envelopes in shirt pockets AND the de riquer plastic water bottle in my hand. Since I don't have a cellphone, sometimes I hold it to my ear and talk to myself like the people in the trendy food stores.

And of course, I keep myself hydrated and the one bottle refilled during the day.

An intitial water supply is just like a basic firemaking kit.
It's there to keep us going until we can build a shelter or secure more water.