It sounds possible from first impressions. I'll give it some thought and speak to some people at work who are better placed academically to do it justice. In the meantime, my one gripe with this and other theories is the length of time the water is actually in contact with the media for. I know the media will become wetted and water will diffuse into the media across the film but I just cant help thinking that not enough contact time is occuring for this type of explanation to be viable. I cant get away from the thought that the actual impact of water on media is more important and this
leads me away from BHM being anything different to lava rock etc other than the fact that it wont erode.