ResMed who makes cpaps recommends distilled to keep the scale down and for the reservoir to last longer. Those are the only two reasons. I get a new reservoir every 6 months anyway.
Ship tap water is fine.
If you are concerned about chemicals, let the water sit for 20mins before you put the chamber in the machine. If you want to clean it less, or want “mind clean” water, use distilled.
I used my humidifier every night. I tried a week without it and found my sinuses did better without the humidifier. I do have sinus issues and had sinus surgery. My sinus membranes get swollen when I use the humidifier. YMMV but a tip for anyone who has sinus issues— maybe try no humidifier.
I still can’t get over that there is a person in this world who travels with a cpap and no extension cord (and I guess no extra outlets either) !!