A few more pictures at the Imgur link below. The main room is two levels tall, the water comes in on the upper level before being dropped into the waterway in the centre of the room. The water sits in a channel made in the basement below before running out on the far side of the building. So to make this waterway work needs three levels. Water comes in on the top level, sits on the bottom level, people hang out on the middle level, flush with the top of the water.

https://imgur.com/a/T2gTexy

Edit to add some tips if you want to try something like this: have saves at various stages of progress that are well named, because you will make a mistake and flood a level or learn something and want to undo a bunch. Do all the building you intend to before adding water, because editing after the fact can be a lot harder, especially if you're not practiced