Bumping this as the previous points seem to be still relevant.

In the past, I’ve used mainly tap water in Japan for my CPAP, as it’s pretty much impossible to find bottled water that doesn’t have minerals in it. For my current trip, I’ve made a harder effort to try and use better water. The best medical-grade water I’ve been able to find is purified water that’s found in the eyecare section of larger drug stores. Here’s a picture in case it helps anyone else in their travels.