"Do you believe humans have been drinking 2-3 liters per day historically?"
Why not? Humans generally avoided arid climates until fairly recently, so I wouldn't consider the idea of drinking 2 liters per day as absurd on its face.
Also, one of our killer features is the ability to cool our bodies down by sweating. That makes us incredible endurance hunters, who can eventually exhaust even much larger and faster prey by simply following it around until it collapses from excess heat. But that requires drinking water.
So, hunters carried 2-3 liters of water during hunting? Have you seen in the museums the water pouches made from leather? They barely hold a liter to a liter and a half. Even the ones I've seen made from wood barely hold more than a liter. I doubt people always hunted close to streams so that they didn't need to carry water with them.
Depending on where you live, you will sweat out a lot more water on a daylong hunt.
But in semi-arid climates, where streams are rare, animals tend to gather around watering holes, so that might actually be the best place to start your hunt.
Why not? Humans generally avoided arid climates until fairly recently, so I wouldn't consider the idea of drinking 2 liters per day as absurd on its face.
Also, one of our killer features is the ability to cool our bodies down by sweating. That makes us incredible endurance hunters, who can eventually exhaust even much larger and faster prey by simply following it around until it collapses from excess heat. But that requires drinking water.