There's some evidence out there that using tap water instead of distilled water in CPAP machines can expose you to Legionnaires' disease because of the harmful stuff floating around in tap water.
Rock Hinkle shared this link that is instructive on this point:
According to the CDC. they have never had a reported case caused by CPAP. They also report that they have never asked in any of these cases about prior CPAP use. Maybe now they will.
When I began CPAP in January, my doctor told me to use distilled water in humidifier and with the nasal irrigitation system. I thought she might be a tad too careful, and checked our our local water system on the internet. There were 3 or 4 pages of chemicals, disinfectants, chlorine - things I have never heard of, and certainly don't care to inhale from either of the systems I use. --- but I usually drink it. I rationalize that my stomach can tolerate it better than inhaling all those disinfectants so close to my brain - It may not be logical, but it works for me. Ruth