I water all my orchids with tap water, which is liquid limestone here, and I've never had a problem with it. Granted, during the warmer months I put most all of them outside and let them get rained on whenever I can, so that washes out most of the salts, but I've never had a problem otherwise.
As far as ferts go, don't think that fertilizers are bad for orchids, they need their food too. What you want to do is dilute the fertilizer to 1/8-1/4 strength and feed them that way. Full-strength can fry the plants, no doubt, but I wouldn't withhold fertilizer completely.
My Phalaenopsis and Oncidium are kept indoors during the winter with no extra humidity, and again I've never had a problem with it. Some of my more sensitive species (Masdevellia, Neolehmannia, etc.) are kept in a humid terrarium, but the others don't get any misting or humidifying at all. And the ambient humidity inside my house is somewhere around 2% at the moment. Humidity isn't terribly important for the more common species.
The main thing to remember is that most orchids are epiphytes, and thus will never be soaked for more than a couple hours in nature. Overwatering is the easiest way to kill an orchid, so very well-drained medium is very important.