The effects of a non-Boussinesq fluid are discussed for Rayleigh-Bénard convection in a cubical cavity with perfectly conducting side walls at low and high Rayleigh numbers using water as a convecting fluid. Non-Boussinesq simulations were calculated with a variation of 62% and 40% of the thermal expansion coefficient and viscosity, respectively, between cold and hot plates. These variations are well above the 10% usually accepted to consider the Boussinesq approximation. The overall laminar and turbulent flow topologies obtained are not significantly affected by the effects of the physical properties variation with temperature.