No way i have heavy metal problems with my Rhino. I use distilled water with him and alsways have . we have spring water not well , BUT it is still hard water so i don't use it . As far as humidity , its a balance trying keeping it above 60% and not get mold in your home . I am not sure that my Rhinos problem didn't start because i was keeping it too high and MAY have had mold issue . never saw any though and tried NOT TOO . I WAS using indoor carpet but added linoleum a month ago and a fan . So who knows .