As with most concepts, the theory is good, the reality isn't. Water is the mortal enemy of these units. In an industrial setting, this concept is totally impractical and down right fatal to the business if one mistake causes water to get everywhere. Every board that gets touched with water is bricked and your investment is down the toilet. Air flow is how these units were meant to operate.
This is a false claim.
Water cooling is safe when you know how to do it properly.
In Russia they are actually taking advantage of the heat produced by miners, and they have built water cooled Bitfury-based miner (Sunrise series).
So those miners are not only mining btc, but also working as 'water boilers'.
See RMC (Russian Miner Coin) for more information about that case.
They have some pictures of the water cooling builds at their Facebook page.