Being dry fasters, we now have access to much more water than we did when we were not dry fasters. So I too think that we don’t need quite so much water. The fat that we eat also has water in it. I eat a 96% carnivorous diet with a lot of fat and butter, so drinking water is not such a big deal for me now.
I think it depends on the person. I naturally need to drink 2 - 3 liters a day maybe even upwards of 4 if I’m working out a lot, but I also sweat more than anyone I know. Ever since I was a kid I was prone to heat exhaustion and dehydration.
If I don’t move around too much and try to keep cool, I do ok with dry fasting. But like, a brief walk could work me into a sweat (and I’m not overweight or unfit– literally just sweat a ton).
Those people have archaic information. Just keep your pee at a healthy light yellow colour when feeding and you’re golden. Look into tap-water vs. distilled+minerals vs. high-grade mineral water if you want to optimise, but that’s probably not essential. When w.fasting, same rule applies about your pee as above; when dry-fasting, you can go for at least a couple of weeks if you’re sensible about how you do it. Drinking your pee is a good way to tell how hydrated you are, when feeding: it becomes delicious after a while, like becoming accustomed to the taste of alcohol, and is in moderation pretty good for you (I think subbing all the fresh water you would otherwise be drinking for pee though may be over-doing it as I think fresh water has a very beneficial flushing and cleansing effect) and then you just know by taste if it‘s too strong or too weak.