I don't remember anything about lack of water. For example, nothing about bathing as a signifier of social class. So I guess it's possible that the spire is pretty efficient at just recycling the waste. The waste gets the water drawn out and recirculated and the solid matter gets sterilized and used as fertilizer (vatsand). There appears to be enough available electrical power and, presumably, previously available biological knowledge to set up such a reclamation system. How much it runs without intervention and how muc hthe spires inhabitants maintain it isn't mentioned anywhere.
That would explain where (most) of the water comes from and where (most) of the poop goes. Both very important things to cove when any large population gets discussed.
Of course, without rain, I'd guess that street cleaning / garbage removal / etc has got to be a pretty big deal. No mention of how lower class sections of the Habble constantly smell of poop, rotting garbage, etc. One good outbreak of Cholera or something and you can't just wait for the rain to come and clean things up a bit. You have to go and scrub all that down by hand.
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Of course, if the Predator is self aware, what about the spires themselves? Do they live in the
self aware colony?