Similar to the water:piss ratio regarding (US?) swimming pools, insofar as the knowledge that the “nostalgic” smell of swimming pools is not the comforting presence of chlorine so many believe it to be, and is in fact the confirmation of a volume of piss in the water that is rapidly nearing the extent of said chlorine’s capacity to neutralize (sapped also by ceaseless sunshine & innumerable contaminants hitching rides on patrons’ oblivious meatsacs).

In short: if you smell “pool”, someone(s) have pissed in it. A lot.