The main objective of the paper is to predict the optimal waterjet pressure required to cut, drill or debride the skin layers without causing any damages to the organs. A relationship between the waterjet pressure and skin thickness has been established. It also includes the modulus of elasticity of the skin, the diameter of nozzle orifice, the nozzle standoff distance and the traverse speed of the waterjet as well as the duration of applying the waterjet pressure. Thus, practical relationship between waterjet operating parameters and the physical properties of the skin has been formulated. A real Caesarean section procedure data has been applied to the formulation. Given the Ultimate Tensile Strength of the skin at the abdomen to be 20 MPa, incision parameters of 18 mm deep, 12 cm long and 0.4 mm wide, applying a traverse speed of 0.5 mm/s and stand-off distance of 5 mm, the resulted waterjet pressure is 17.89 MPa using a 0.4 mm orifice diameter.