The expressions for density and fraction of H-bonding H atoms are derived and applied from supercooled to superheated states of liquid water (H2O). The anomalous density variation (around 4 degreesC) with temperature is explained solely on the basis of H-bonding and non-H-bonding (NHB) H atoms in the liquid. Interesting structural changes are postulated as the temperature of liquid water increases from a very low to a very high value. The limits of supercooling and superheating temperatures are calculated to be around 180 and 980 K, respectively, at 1 atm pressure.