Now, the exiting o2 goes through that big pool of h2o above it, using gas radiant pipes. (Aluminum ore is best for this in midgame, but in this case I used some wolframite.)
The h2o came from the cool h2o we start with, which I carefully gathered and protected very early on in the game. Later in midgame, we'll run out of it, and we'll trickle in some hot water, that cuz it's in such small quantity, won't overstrain the system.