I'm not saying one gallon is optimal or even bearable. But it is survivable under the conditions currently in the region.
I hear you about the heat, but reality was that I used more water in the winter than I did in the summer. I attribute that to the much larger caloric intake in the winter. 4000+ a day requires some cooking and cleaning. And the body requires water to process that much food.
Wilderness living is hard. I did do it. For over a year. I don't do it, today, unless required. ;)
/johnny