Separation of the real (n) and imaginary (k) parts of ATR-FTIR reflectivity spectra via the subtractive Kramers-Kronig transform allows for qualitative analysis of silica colloids with different densities. Normalized absorptivity index (k) spectra were used to create difference spectra that reveal how the water structure in each colloid differs from that of bulk water. Utilizing this method, it has been shown that there is an increase in strongly hydrogen-bonded water at low colloidal silica densities, and a decrease at higher densities. These observations can be explained in terms of the disordered/ordered phase transition of colloidal silica as a function of particle density.