So far as I’ve known, no one has used custom water meshes and I have no idea how to set it up correctly.

Are there specific steps I don’t know?

Does custom water meshes need a surface plane?
Or can it work like the beach waterfalls where they are curved?

This component may be broken in a way or just somehow make it less complex or add instructions on how you should handle certain values with other values correctly.
Like I said, no one in the Gtag modding server knows how to set these up properly.