The excess partial molar enthalpy and the excess chemical potential of 1-propanol in ternary systems 1-propanol-(1,2- and 1,3-)propanediols-H2O were determined. The enthalpic interaction function between 1-propanol molecules was evaluated. The mole fraction dependence of the 1-propanol-1-propanol interaction function was used as a probe to elucidate the effect of 1,2- and 1,3-propanediols on the molecular organization of H2O. Together with the earlier similar works on 2-propanol and glycerol, we conclude that the hydrophobic moiety diminishes the hydrogen bond connectivity of H2O by reducing the hydrogen bond probability of bulk H2O, while the effect of the hydropbilic moiety is primarily to reduce the degree of fluctuation inherent in liquid H2O.