If there is a waterlogged stair upside down and there is a transparent block below it, the water cannot be seen from below (as seen in picture). Is non-directional from my testing.
How to reproduce:
- Place stair in such a way that there is an "empty" area facing down.
- Place a transparant block, such as a barrier or glass, 1 block below the stair (no air gap).
- [Optional] For a cleaner setup, surround the blocks around the stair so that the water doesn't flow out when you do step 4.
- Waterlog the stair.
From beneath, it looks like the stair is not waterlogged.
From beneath, it looks like the stair is waterlogged.