I used to have a mental block to growing any orchid in water, but saw people from beginner to professional have tremendous success with sitting their phrags in water. Now I grow in s/h, where everything sits in water, go figure. The water gets replaced about once a week. Sometimes even less frequently if I'm busy. I can tell you that all phrags except the long-petalled species *love* s/h and most of them have roots growing directly into the reservoir. That includes besseae and its hybrids. They love water.

It's not "natural" to keep them in purportedly stale water, and Peter is correct in that many of the species grow in constantly-flowing water, be it a river bank or on a cliff with constant water seepage. But keeping orchids in pots is not natural either, nor I suppose is the concept of growing phragmipediums anywhere except South America. But I think the greatest wrong one can do a phrag is to let it dry out.