For humidity and misting, I always used the cheap bottled (distilled water). I have very hard water in my area and I do this not so much for the Cham, but as the others above say, to keep my stuff from getting clogged up. We have VERY hard water. I need to add a filter for my refrigerator (on top of the fridges filter) because in a mater of 6-9 months, the water dispenser stops working due to mineral deposits clogging it up..
It's very cheap by the gallon from any discount big box. I pay about 79-89 cents per gallon at Walmart.