> I'll change the highway from "water_path" to "path" for now, those ways were meant to indicate traffic flows within a pool area, both after exiting a water slide and for approaching stairs. Is there a tag that I can use to indicate that the path is used for these purposes, or simply to indicate that they are paths within the water? 

I'm not sure those are meant to be tagged, a pool is inherently unroutable since it's a body of water, and I don't know of a standardized tagging for "suggested paths through water". Probably the best thing to do is look up other waterparks and see what tagging they have.

> (which this tag is also not listed on the wiki for highway, should I change it?),

No, the wiki should only be changed if there's a large usage of the tag
