I was out north of Kal last Sept. The temp only got to mid 30's by midday. Went out around 8am & wandered around turning gold into iron (& cupla tiny iron bits into gold) for around 6hrs. It wasn't extremely hot, but very dry air, & I was drinking about 1L/hr. Forget the people that say you need about 2L/day.
& Im not big on salt, but when you're losing that much water in a day you are also losing salts! I find a can of baked beans in the arvo good. Bit of protein, carbs, & salt. But any mildy salty carb loaded canfood is a good recharge.
A reminder about how long you are out vs how much water you drink.