Using a wind tunnel the evaporation rate of water at normal temperature and pressure was measured as a function of temperature, humidity, air velocity, and diameter of the vessel. In order to measure the temperature of the water surface and the boundary layer on the surface, the temperature above and below the surface was measured as a function of air velocity with a thermocouple of 0.076 mm diameter. The present experimental results are in agreement with the present theory for a laminar flow, which is based on the idea that the evaporation rate is equal to the diffusion velocity of water vapor in the boundary layer. For a turbulent flow the experimental evaporation rate was found to be proportional toU0.86±0.03, whereUis air velocity. This is consistent with the velocity dependence of the experimental thickness of the boundary layerd, which wasd∝U−0.90. A new semiempirical formula of the evaporation rate is proposed. ©1995 American Institute of Physics.