Hydrostatic body fat testing measures body mass under water. You weigh on land first and then in the water with a special weighing tank. After controlling for factors like water density, lungs volume, and body density, you get your body fat percentage calculated. This method has advantages and disadvantages.
Hydrostatic testing for body fat is more accurate than other methods, including such as skin fold calipers or electronic devices (bioelectrical impedance) and has the reputation of being the best and most accurate method.
For those with pacemakers, hydrostatic testing is an alternative to electrical impedance devices. A person with a pacemaker cannot be tested using an electrical device because it could cause a pacemaker malfunction.
For athletes, hydrostatic testing could underestimate real body fat percentages. In seniors with osteoporosis the test may overestimate the measurement.
Hydrostatic testing requires that you stay very still while under water. This can be difficult and can cause panic in some people. You must also go under water several times for best results, which could be stressful for some people.
Access to Equipment
Hydrostatic testing equipment is expensive, so you may not have access to it. Most likely, only colleges, hospitals, research facilities or sports organisations will have the equipment.