An experimental and numerical investigation is presented concerning the transient and steady-state natural convection of water through its density maximum in a rectangular enclosure with the vertical end walls held at different temperatures. The water in the enclosure is initially at a uniform temperature above the density maximum at 3.98 C, and then the temperature of the cold wall is suddenly reduced to and maintained at 0 C. Experimental flow patterns are presented for 5 and 8 C initial and hot wall temperatures. A pH indicator technique is used to visualize the convective flow patterns in the enclosure. Numerical solutions of the convective flow patterns are presented for transient and steady-state natural convection, and are shown to be in good agreement with experimental flow patterns. The effect of the density inversion on the transient convective flow patterns was dominant at a 5 C initial and hot wall temperature. Steady-state results for an 8 C initial and hot wall temperature show an asymmetric convective flow pattern with the dominant flow cell being above the density inversion.