i didn't really reference any specific real life installations for most of the dungeon. I mostly looked at infographic diagrams of plants by searching "water treatment plant diagram" and "waste treatment plant diagram" to get a sense of what major parts of those things have and what would be the path waste would flow. The purification cistern, though, is based on the Metropolitan Area Outer Underground Discharge Channel in Japan which is a huge flood water diversion facility near Tokyo, and the sorting hall is based on a medieval great hall, the Winchester Castle great hall is a pretty decent reference but just with big long work tables where the gnomes sort the trash. Also all the sizes here are kinda loose since it is all for gnomes, so it could be smaller than it would be realistically cause the gnomes are small or it could be even bigger than irl cause there's A Lot of gnomes.
