In Reply to: Can This Be For Real? posted by Tunnel Rat Richard on September 14, 2005 at 14:59:03:

Dissolved oxygen in cold water runs about 6 parts per million, less in warm water. The volume of water that would have to be processed to supply a diver with enough air to breathe is enormous. The air we breathe is ~200,000 parts per million. To supply the equivalent of an 80 cu. ft. tank of compressed air would require that you take all the dissolved O2 out of 533,333 cubic feet of sea water. Highly impractical.