Some notes on the design: The design basically works with older versions (1.8.9 confirmed), but has an annoying issue: lava sometimes flow back and destroys the water source block. A small alteration makes this issue handle easy: make the base platform one block bigger on the wide side (5x3) and place the water source block two block far from the opposite wall. The falling lava normally generates smooth stone.
When lava flows back, it generates a cobblestone that blocks the water from flowing (but at least does not removes the water source). you have to place a block (e.g. a cobble) to the place of the stone, and remove the blocking cobble. Wait until the water starts flowing again and remove the placeholder block below the lava.