Water per orchid? I never thought of tracking such a thing. I usually flood every orchid I water...Overwatering is caused by watering too frequently, not the amount of water that is given at any one time.
As far as bottled water...Distilled is fine but most drinking water has Sodium added. Where I live in Fort Worth we get fairly soft water from Eagle Mountain Lake. If you are concerned about your tap water, you can get a TDS meter. I only occasionally use rain water..most of the time even my sensitive orchids (Milts, etc.) are watered via the tap.