A reflective THz imaging system sensitive to small variations in water concentrations has been developed. Biological tissues such as skin, eyes and teeth were imaged to ascertain the systems response to tissue hydration. Difference in water concentrations translated to contrast in the THz images. Contrast was also seen in THz images of skin cancer and burns suggesting the potential diagnostic capability of THz imaging system in clinical settings. All specimens analyzed were freshly excised ex-vivo tissues. These encouraging preliminary results have motivated us to explore the in vivo potential of our imaging system.