Hi, I made that video, I know things about these brakes and how they perform with water.
You may as well not water bleed your brake if it's in warranty, but a lot of people don't mind and do it anyway.
Common misconception is there is shit in a brake that will rust. It's not true, mine works fine water bled, all of mine have.
Some people's levers develop a stiff master cylinder. This is rectified by pulling it out and lubricating it underneath that seal. Some people never have this happen to them either.
Also, if you use antifreeze in there, it also won't destroy the seals. Otherwise my brake would be completely knackered.
Water bleed if you like, it's good because it's free, it's easy, it won't kill your brake, and it can produce a quicker lever feel.