Understanding water dynamics at material interfaces is crucial for applications in biotechnology, electrochemistry, and energy systems. In this study, we employed Fourier transform infrared spectroscopy and electrochemical quartz crystal microbalance with dissipation monitoring to investigate the hydration states and ion interactions of functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films. By applying controlled potentials, we monitored ion absorption and desorption while using Gaussian fitting to analyze the O-H stretching bands. Our results revealed that sulfate ions (SO) compete with water molecules at PEDOT interfaces with hydroxyl groups, whereas perchlorate ions (ClO) exhibit minimal interference due to their weak water interactions. For PEDOT functionalized with zwitterionic phosphorylcholine groups, higher levels of intermediate water and nonfreezing water mitigated dehydration in saline environments. This work highlights the synergy between electrochemical and spectroscopic methods for real-time analysis of ion-water-polymer interactions, providing critical insights into interfacial phenomena regulated by applied potential.