I haven't got RO water, but there have been many discussions over the years. Should be fine provided you fertilise your orchids.

In nature I suppose the orchids get a tiny amount of nutrient from rainwater running over tree branches and rocks or through accumulated detritus.

Do a R O Water search to find past discussions.

Lightning will separate nitrogen from the atmosphere which is then absorbed by rain and transferred back to the ground.

RO is good but I would add a fertilizer that contain some minerals.

How far away are the orchids from the ro unit? Maybe some tubing to use like a hose? On mine with the pressure tank the water pressure is not high, the water could be stopped with a thumb on the hose.

I set up an outdoor ro system this last summer, made a tremondous difference fo the orchids. My tap water is very hard, it kills orchid plants just by wattering them. (ABOUT 1000 PPM)

Charles my little RO tanks are pressurized and between the one gallon hudson type sprayer and the watering cans it is not hard to fill them up and take them over to the orchids 20 feet away.

1000 ppm that really is hard, it was smart of you to set up the outdoor system, I bet your orchids are much happier now!