As an extended lunch break from Prague, I visited the wastewater treatment plant in Bubeneč. The plant lies on the banks of the Vitava (Moldau) and is situated at the lowest point in Prague. Seeing that sewage needs to flow, building a wastewater treatment plan here was the sensible thing to. So sensible indeed that the modern wastewater treatment plant built in communist times is situated just across the river.
Thankfully the communists didn't tear down or redo the old plant, so Bubeneč has retained much of its original setup. The steam engines are still operational and are turned on occasionally. However, it's not longer connected to the sewerage, so you don't have to worry about smells. At the time, when all of Prague's sewage passed through, it must have smelt terribly.
The facilities are nice to explore. They offer tours, most in Czech, but you can ask questions in English. In addition, they pass out a guide. Small tip: Just read the guide before you go on the visit and put it away. You will be busy with your camera anyhow... The site is very photogenic emanating a quirky 30s, Metropolis charm. And it's quite interesting to see how a treatment plant operated.
OUV
The Czechs are very good at finding niche topics that have OUV appeal; Kladubrny . Wastewater treatment, sewerage, and safe water were key developments to make cities safe and extend human lifespans to where they are now. It's telling that we judge countries on the safety of their drinking water. And we consider civilization to break down, as soon as the water supply breaks down. Well, catching Cholera is one experience I can do without.
I can't judge, though, if Bubeneč is the best/earliest example to use. Without a comparative study this is hard to tell. What I did pick up from the guided tour is that a similar plant was built in Frankfurt first, but has been demolished since. In my native Hamburg, you will also find a water filtration plant from the same period. The Wikipedia article on the history of water supply and sanitation lists plenty of places, but not Bubeneč. The Bubeneč Wikipedia article, meanwhile, is a stub. I think ICOMOS should review and find the best candidates first, before any sites are inscribed.
Getting There
It's well within walking distance of Prague old town.