In this communication, we show that the combination of the coupling hydrogen bond (O:H-O, or HB) cooperativity and polarizability (HBCP) premise with the bond order-length-strength correlation and nonbond electron polarization (BOLS-NEP) notion governs the performance of the undercoordinated HB and the size-dependent functionality of water droplets. With the aid of perturbative differential phonon spectroscopy (PDPS) and the extended Grüneisen function , one can correlate the performance and functionality of water droplets effectively. The PDPS proceeds by subtracting the spectral peak of the bulk reference from those of the sized droplets after all spectra are peak-area normalized. The normalization eliminates errors or artifacts of experiments. Table summarizes the formulation and indication of the mentioned regulations and approaches.