We extend to heat capacity C-p the model of Vedamuthu, Singh, and Robinson (J. Phys. Chem. 1994, 98, 2222). This model and that of Bartell (J. Phys. Chem. B 1997, 101, 7573) fit successfully, even in the supercooled region, the temperature dependence of C-p volume, and isothermal compressibility k(T). The Robinson model is superior for k(T). Tanaka's model (J. Chem. Phys. 2000, 112, 799) fails for C-p even after correction of a derivational error. All three models assume that the liquid consists of low-density component 1 and high-density component 2. We conclude that Robinson's tactics, ignoring the intercomponent equilibrium constant and determining compositions solely from volumes, yield the most reliable compositions and individual-component properties. Our fits of the Robinson model to C-p yield at 0 degrees C H-2 - H-1 of (135 +/- 35) J/g, H-1 - H-ice of 0.8 Delta H-fus, and C-2 - C-1 of (0.1 +/- 0.7) J/K center dot g. The enthalpy difference between the components is largely responsible for the rapid change of C-p at the lowest supercooled temperatures. We propose an adjustment to Speedy and Angell's (J. Chem. Phys. 1976, 65, 85 1) experimental values Of k(T) for supercooled water.