Boiled water won't matter at all (presuming it's at room temperature when you are misting!). There's quite a debate about distilled water which you can search on this forum - I'm not jumping in the middle of it. I use purified water (gallon jugs from the store) in my Mist King. The reason is that I have a well, and prior to the purified water I would have calcium buildups on my sprayer heads. It was a huge pain to clean them, but I haven't had any trouble since I switched to purified. Good luck!