Ahh, well then, i think that you can only change water transparency. In classic the water does not allow to see beneath it, in reforged i don't remember correctly.
For the water transparency keep in mind that it will change all the water on the map, there is no way to make only a portion of it.
You can use a trigger that changes water transaprency only when elevator should be seen.
Or you can make a more complicated thing.
Download a custom water model. I remember there is one, that is just a square with water texure animated on the surface.
Set the transparency of the game water to 100% so it's invisible.
Create a doodad (make sure it's walakble and has no collision ) with the water model, and then you will have to place the water doodad one by one. You can set the height of doodad with PagUp and PagDown if you need.
Then make a trigger that detects if a unit is near an elevator and make the current water square transparent. This way the elevator will be visible but not all the water in the map will change transparency
Check this out
[Terrain] Advanced Water Effects