Unknown texture showing up in the water when placed above slabs

I was creating a pool for my friend but suddenly i discovered something unusual that after I placed all the slabs for the stairs I have been seeing the texture of mossy ston bricks when water is above stone slab and smooth stone when placed bove cobblestone slab. I have provided a video that only contains about teh stone slabs showing mossy stone bricks texture in the water. Hopefully this report will get an urgent response