Electrical bioimpedance was measured in 7 body segments, and also with the standard right-side method, using 11 electrodes at 6 different frequencies in 8 healthy male subjects with similar anthropometry. Our objective was to determine the capability of segmental bioimpedance measurements to estimate small changes of water on each segment (TWsegi)and total body water (TBW) in comparison with the standard right-side method. Water was also estimated with 40K and DXA. Volunteers were measured before and after a 3.5% water load of their individual TBW. The expected TBW mean increment after water load was 1.45 l. The estimator with lower Standard Error SE was the weight of the subject (0.15 l). For impedance methods, the SE of the segmental method was 0.94 l vs. 1.41 l for right-side. Segmental volume changes obtained by DXA and Impedance compared with expected values showed maximum differences of almost 2 l for DXA and 0.5 l for Z in the abdomen. In conclusion, in a healthy sample with similar anthropometry, such as astronauts and athletes, the use of a segmental impedance method improves the accuracy of the right-side method to estimate TBW. Changes in water segments estimated by impedance where more close to expected values than using DXA.