My husband and I spent two months housesitting in London this winter, which was a delight--and a great way to explore on a budget. As I mentioned earlier however, traveling with a CPAP machine can be a challenge, since many airlines count a CPAP machine as a carry-on. But what was even more challenging was finding distilled water for my humidifier there! I visited and called grocery stores and pharmacies, even a formulary chemist associated with a hospital, and none of them offered distilled water. Eventually, I bought some on Amazon UK for a horrendous markup. Stores in the U.K. do sell de-ionized water, but having read on the Internet that de-ionized water only has impurities and minerals removed, but is not sterilized for bacteria, I didn't feel safe breathing humidified air with the de-ionized kind. I'm still researching this because, unfortunately, there is a lot of bad information on the Internet, but I will do my best to find out the best water sources to use, and I'll let you know, with information from trusted medical professionals. Some machines can be used without a humidifier too. However, tap water should never be used.
What I didn't consider, but realized later, was that I could have simply purchased the easy-to-find deionized water and have boiled it to purify it (one minute, or up to three minutes at higher elevations). When cooled, it would have worked fine.