I think it was during Niku IIII in 2001 when I was deployed to the 7 site for clearing operations, I ran through near 200 oz of water in one day. I know because my Camelbak bladder was 70 oz and I filled it and drained it three times, or nearly so. And that was out in the field, and didn't count what I drank during breakfast or after returning to the boat (beer is God's way of telling us he loves us). Most of that water ingested came out in the form of sweat, we were soaking wet from head to foot. I think I only pee'd once the entire day which should give you an idea of how much sweat we produced. Two quarts a day would not cut it for any kind of extended period involving serious work.
This was early on in the expedition and we were swinging machetes, not chainsaws and pneumatic loppers as during later expeditions, and water consumption is always higher before we acclimate to the heat and the work, but I think it is a good illustration of how one can need significant amounts of water when trying to accomplish physical labor on Niku. It also highlights why water was so critical to the success and ultimate failure of the colony there, and would have been critical for a castaway. Of course if you sat around all day and only became active at night, the demand for water would be significantly different.
Andrew