I used to, but in many of the places we've travelled in recent years I haven't always been able to get it.

In it's absence my preference has been for rain water, but that hasn't always been available either, so at times I have had to use either bore water (at our current location since May this year) or filtered river water (at our previous location - September 2 to May this year).

I did wonder if I might get deposit build up on the humidifier's heater plate, but so far ....... none. I occasionally put a drop of Eucalyptus oil in the water, just because I like the smell.

My spouse used a Fischer & Paykel CPAP. Water was held inside a plastic container and liquids never made contact with the heating plate. She just used tap water and rinsed and cleaned it routinely to avoid any build-up of bacterial agents.