I don't remember suggesting that you breathe in that dust or indeed any dust.....
BTW if the brake is hot enough to boil the water, the dust is likely to emerge as, er, dust, and if you are purging it out as you go, you might (more than normal) be breathing it in as you ride, depending on how the airflow is arranged over your machine.
Every ~18g of water you add turns into ~25litres of gas at STP, and a much larger volume than this at higher temperatures, obviously.
Another thing that may happen is that the various pivots and cams inside the brake may be stripped of lubricant more quickly than normal, if you are regularly 'steam cleaning' the inside of the brake. Keeping these happy, long term, is difficult enough in the normal run of things (the lubricant has not to melt or pick up dust too much, amongst other things) and this may not help at all.
BTW I have experienced saturated brake linings in these brakes and have also seen thermal fatigue/shock damage in similarly treated parts. But what do I know, I'm only a fully qualified materials scientist with several decade's experience.... etc etc etc....
cheers