Define drawbacks for underwater weighing method?

Since the major drawbacks with UWW method are that the subject needs to be totally submerged underwater and exhale all of the air in his lungs, body volume and body density can be measured by Air Displacement Plethysmography (ADP) as an alternative. For this measurement, the subject sits in an air-filled chamber, which is attached to a reference chamber of a known volume. The subject's residual lung volume can be measured while in the chamber.

The major advantage of ADP is that the subject does not have, to be submerged underwater, and it takes only a few minutes to complete. At present, there is only one commercially available ADP instrument, called the Bod Pod and its software is still based on the 2-C model. The ADP technique is rapidly Yeplacing the UWW approach as the preferred method for the measurement of body density.