It's fine you thinking what you like of it, Janne.
Truth is, we are entitled to our own facts, in the end
But, I don't think it is wrong.
Just for example, as a source that might convince you, go on any of those forums that deal with sojers talking about dealing with the heat being in Afghanistan - like ARRSE, though esp. one of the US ones. There is water everywhere there, stacked in pallets feet high everywhere, and they are encouraged to do the drinking of it. 2 gallons plus, plus, plus per day. Not that they need encouraging.
When you are exercising in the heat, you can drink a gallon a day and still get brown pee, like Santa says .... you just need to drink more. Because it is the skin, which is a gigantic and demanding organ, that is dealing with the water for the priority of cooling ... the kidneys are in the second order of things
This is I think quite conservative:
https://www.tripadvisor.ca/Travel-g...alifornia:Staying.Hydrated.In.The.Desert.html
...but it gives a clue, especially the bit where it says: "A 150 pound person in arid hot conditions, who hikes for 20 minutes or changes a tire, needs about 90 ounces (3L) of water a day".
I guess most of us are over 150lbs and do more exercise than hiking for 20 minutes.
There's an online calculator in that article
http://www.csgnetwork.com/humanh2owater.html .... it is again, I think, conservative. It suggests 4.2L per day for a 90Kg/200lb person taking one hour of exercise in the warm (walking with a pack I reckon that means, not throwing straw bales onto a truck); just one hour.
But even Uncle Ray's films TV programmes explained all this (citing 20L per day for an active soldier in the heat) and you can ask any athlete or outdoorser, they'll say the same, (probably whilst rolling their eyes, in the sanctimonious way they sometimes can
).