WATER: RO, Rain Water, Misting, Watering

[HDCochran]

I have a 25 gpd RO unit and have recently moved from a 2'x4' orchidarium to a 12'x12' greenhouse. I find I need much more water to raise the humidity. I also found that even with vents, exhaust fan, and shadecloth I need additional cooling in the summer. I have excellent air circulation. I do not now have the ability to collect rain water but might be able to do this in the future. So, I have several questions as follows:

1. If I mist under benches for cooling during summer, should I use RO/rain water or is tap water ok?

2. Can I also use tap water to raise humidity?

3. Can I use RO/rain water interchangeably for watering?

I will be very grateful for answers or any other relevant advice.