Aqueous Zn-ion batteries (ZIBs) are emerging as safer and more sustainable alternatives to traditional Li-ion batteries. Among the critical components of ZIBs, the electrolyte plays a key role in determining electrochemical performance and battery efficiency. However, conventional aqueous electrolytes pose challenges for Zn anodes, including poor reversibility and limited cycling stability caused by dendrite formation. To address these issues, "Water-in-Deep Eutectic Solvent (DES)" electrolytes have garnered attention as eco-friendly and cost-effective solutions. Despite their promise, fundamental questions remain unanswered: the optimal water content in DES, the effect of water on electrolyte dynamics, the disruption of DES hydrogen bonding networks, and the changes in the Zn²⁺ solvation structure in water-in-DES systems. Using ultrafast 2D IR and 2D NMR spectroscopy, we investigate solvent dynamics, structural rearrangements, and hydrogen bonding behavior across varying water concentrations, both with and without Zn salts. Complementing these experimental methods, molecular dynamics (MD) simulations provide insights at the molecular level. Our findings reveal that adding 10 moles of water per mole of DES optimizes electrolyte performance, as confirmed by peak conductivity in impedance spectroscopy. These results offer valuable insights into improving ZIB electrolytes and enhancing their practical applicability.