when you meant by: "Give a small space between the glass brush and the terrain patch with the water texture. Set all faces of the glass brush (other than the side facing the room) to the texture "no draw""
I should replace the glass brush with to "no draw" While leaving a small space between the brush and the patch?
And for the 2nd solution I don't think that would work, because I don't think water is meant to be flipped vertically I might justify this from placing the water horizontally which will work Example:
Note that there should be glass brush above the "lava brush" which appenrently doesn't show when your outside of the water but when entering noclip you would see it. Obvisouby I will put a clip to the borders but thast is a problem to fix another time.