Thermocapillary convection had not been observed in water until the evaporation experiments conducted by Ward and Duan. Temperature discontinuities have been observed at the liquid-vapor interface during steady state water evaporation. Below the liquid-vapor interface, an uniform-temperature layer has been found. A hypothesis is introduced claiming that the uniform-temperature layer results from the thermocapillary convection and buoyancy. The hypothesis has been examined by comparing the liquid temperature profiles of two series of experiments. The uniform-temperature layer was observed when the thermocapillary convection and the buoyancy were both presented. Otherwise, the uniform temperature layer is not observed.