Hydrostatic weighing or hydro-densitometry, one of the older ways to measure body fat and despite its widespread use, is since recently NO LONGER the “gold standard” among scientists.

The overall accuracy of laboratory densitometry usually is 1 to 2 percent and not the theoretical 3 to 4 percent as so often assumed.

Today the four compartment (4C) model is the “gold standard” for body composition and measures four variables: body mass, body volume, total body water (with a solution of isotopes: hydrogen-oxygen) and mineral mass (with DEXA scan).

The good part of underwater testing is that error margins are fairly constant for the average male/female. Here again distortions emerge when body builders or skinny individuals are tested.

Body density varies enough between races, ages, gender and athletes making it a technique that should only be practiced with the right equipment and by experienced professionals. That excludes the portable underwater weighing systems.

The entire body is submerged in a tank of water. That will cause a certain amount of water to be displaced and it is this amount which will be used to determine body DENSITY (not body fat).

Body density is then converted with mathematical formulas into a percentage.

Some universities use this method for their athletes and for a fee they could let you undergo the test too. Fees are $20 to $75.

Remember that it can take as much as 30 minutes and that you have to be submerged in water. Not suitable for the elderly and certain patients. There are more comfortable procedures than hydrostatic weighing to measure body fat for them.