This work deals with design and evaluation of water-cooling system for an electric motor. Theoretical background is given on subject of heat transfer, fluid mechanics and computational fluid dynamics. Review of existing water-cooling designs is performed. Detailed analysis is performed on two existing prototypes, which form the basis of design for our own water-cooling application. Mesh independance study is performed and effect of turbulent models with wall functions for low Reynolds number flows is validated. Furthermore, the effects of geometry and input parameters, such as temperature and mass flow, are evaluated. By choosing the most appropriate values of design parameters better performance is achieved, for instance, pressure drop is reduced at higher mass flow rates and thermal characteristic of the electric motor are improved.