Boltzmann’s energy distribution principle can be applied to liquid water and its vapor. However, for Boltzmann’s principle to be successful, the molar hard core volume of water V-hcH2O(alpha*)(T,p(e)(alpha*), i.e., the volume not available for the motion of the centers of mass of molecules in a mole of water in phase alpha at temperature T and applied pressure P-e(alpha*), must be excluded from Boltzmann’s principle as well as from the equations of state of liquid water and its vapor. The equation of state for water in phase alpha is tau(H2O)(alpha*)(T,p(e)(alpha*) = p(e)(alpha*) - RT/V-avH2O(alpha*)(T,p(e)(alpha*)), where tau(H2O)(alpha*) is the internal tension in the cohesive force bonding water molecules in phase alpha. For pure liquid water, its molar volume is designated V-H2O(l)*(T,p(e)(l*)) so that its molar volume available for the motion of the centers of mass of its molecules is V-avH2O(l*)(T,p(e)(l*)) = V-H2O(l*)(T,p(e)(l*)) - V-hcH2O(l*)(T,p(e)(l*)). At 20 degrees C and p(e)(l*) = 0.023 388 bar, the vapor pressure of water at 20 degrees C, V-avH2O(l*)(293.15 K, 0.023 388 bar) = 3.329 796 cm(3) mol(-1) so that tau(H2O)(alpha*)(293.15 K, 0.023 388 bar) = -7390.51 bar. At 20 degrees C and p(e)(l*) = [0.022 97 - 24.33 06] bar, i.e., reducing the pressure applied to pure liquid water by an amount equal to the osmotic pressure of water in a solution of 1 mol of solute in 1 kg of water, its vapor pressure is reduced to 0.022 969 7 bar, the same as the vapor pressure of water of water in the solution. At 20 degrees C and -24.3076 bar, V-avH2O(l*)(293.15 K, -24.3076 bar) = 3.310 72 cm(3) mol(-1) so that tau(H2O)(l*)(293.15 k, -24.3076 bar) = -7386.36 bar. The applied negative pressure of -24.3076 bar lessens the internal tension by 4.15 bar. Always, when a negative pressure (tension) is applied to liquid water, it lessens (not enhances) the internal tension in the water because the increase in the molar volume of available space lessens the internal tension more than the applied tension increases it. These values exemplify successful applications of Boltzmann’s energy distribution principle and of the equation of state to pure water. The same treatment applies to water in an aqueous solution. As a result, Boltzmann’s principle yields the same equation for the osmotic pressure of water in a solution, pi(H2O)(l), as obtained from a kinetic treatment of Hulett’s theory of osmosis.