Expected ppm of RO water?

[nhman]

So.......after having some, er "issues" with my collection, I got smart and bought a water ppm meter (It adjusts for temperature too! I'd highly recommend this tool for all that use water!)
I found that my home water system wasn't working all that well. (HARD well water runs thru a water softener and then an RO unit.) My orchid watering water was about 75 ppm and I was having root loss and leave death.
So I replaced the water softener and RO unit. I am getting RO at about 40 ppm or so now.
While going about this process, I began "recycling" water from two dehumidifiers in my house (ppm of 0.5 to 10) and from the air conditioner in the orchid growing room. My average ppm in the orchid watering tank went down to under 20 ppm. The plants perked up and looked MUCH better.
The question that I need to know is this - is this normal, high or low? Better yet, is this level of ppm "safe" in watering my orchids????
Advice and thoughts appreciated as always.