Terahertz spectroscopy was used to study bovine serum albumin (BSA) absorption in water over a range of concentrations (0–4 mM). As BSA concentration increased there was a nonlinear change in absorption at 1, 2 and 3 THz, which was inconsistent with Beer’s law. At low concentrations of BSA (0−1 mM), the absorption remained constant or rose slightly depending on the frequency of light used. Above 1 mM BSA, a steady decrease in absorption was observed, followed by a plateau that starting at 2.5 mM. Using a overlapping hydration layer model, the hydration layer was estimated to extend 15 Å on average from the surface of BSA. Calculation of the corrected absorption coefficient for the water around BSA by subtracting the excluded volume of the protein provides an alternative approach to studying the hydration layer that provides evidence for complexity in the population of water around BSA. The light source used in this experimentation was coherent synchrotron radiation from the Diamond Light Source operating in a low alpha mode which generates intense radiation between 0.3−3.3 THz (10−110 cm−1).