The preferred method of calculating body fat composition in my opinion is hydrostatic weighing. It's aim is to derive the body fat composition from the density of the body in water. Equipment such as a hydrostatic stainless steel weighing tank, which requires a special underwater mounted chair and scale.
The person's weight out of water must be recorded, and then with minimal clothing on, sits on the seat in the weighing tank and expels all the air out of their lungs. The person is then completely submerged into the water tank and the underwater weight is recorded. This test must be re-conducted several times in order to determine the accuracy of the result.
Even though this test might be accurate for most people, there are still some disadvantages. One reason for this is that athletes tend to have denser bones and muscles compared to non-athletes. Adding on, the equipment needed for hydrostatic weighing is costly, and the tanks are usually located in universities or research institutions. Thus, making it hard to access for the general public.