About half the B&M's around here are using these Trion 707U auto-filling humidifiers:
http://www.filtersfast.com/Trion-Her...07U-Filter.asp
BUT, unless you are going to run that water through a purifier, preferably DI or a distiller, a good RO system in a pinch (not all RO units are created equal), first, it's probably not a good idea.