My bins hold a little less than a 1/4" of water in them and I have had some problems that may or may not be related to that. The thing I find is that a lot of slime and nutrient deposts build up in there and make the roots all slimy and nasty which probably isn't good for the plants. My veg bins drain completely but my flowering ones hold some water so I try to clean them out after 4 weeks and again before the final flush during every flower cycle.