Those are not counter-arguments. I didn't say "replace all water with money", I meant "keep the amount of water you need" and put the rest into currency. Also, stillsuits.
And you don't need water to douse fires. Just spend one turn to stop it.
It doesn't always take one turn. The game actually tracks temperature (the T:# reading in the sidebar where your stats are also listed). If you are very hot, it takes longer to put out the fire. If you are very, very, very hot, you get flash fired and insta-die.
Some areas later can be comprised of many mobs that all spit unavoidable fire at you all at once, you might not have time to put out the fire without using water while they are advancing on you.
Money is pretty useless anyway. Maybe if your ego is low (very possible if you're playing a melee character) but loot is generally better lbs:value than water anyway. A container of 64 drams is 17 lbs (the container is 1lb, so 4 drams is 1lb), but at ~24 ego a 5lb steel weapon might be worth 25 or 30 drams, you can quickly buy out everything useful on a vendor, until they get restocked, and they rarely have anything that is highly useful and very expensive. I think the most expensive thing I bought was a 5 AV fullerite flake armor, but it was 90 lbs and severely cut into what I could carry around. I opted to use a 5AV -5DV carbide plate instead, which was only about 30 lbs.