When placing a wall in the top layer of water with a solid block in the north-west corner and another wall south of it the water will show a cobblestone texture. Any walls south of the original wall, except for the last one in the line, will also show the cobblestone texture if there is a stair block above, the first one does not require a stair. If there is a solid block on the west side of the wall it does not show this behaviour

And a  larger sample