Most of chemical reactions are performed in aqueous solutions, which are conventionally prepared using laboratory -ready and environmentally friendly deionized (DI) water. Water is generally considered as a passive reactant or as a spectator solvent. In this work, we demonstrate the added reagents for reactions in aqueous solutions can be effectively reduced by utilizing plasmon-activated water (PAW) with reduced hydrogen-bonded (HB) structure instead of conventional DI water with strong HB structure. For electrochemical reactions performing the similar currents the electrolytes used in PAW-based systems are ca. 90% concentrations compared to those used in DI water-based systems. Moreover, these concentrations used in PAW in situ-based systems can be further reduced to ca. 80% of magnitudes for maintaining the similar current levels. More interestingly, the recorded current of oxygen evolution reaction (OER) on a catalytic Pt electrode in the PAW-based system (0.09 M KOH) is significantly higher than that in the DI water-based system (0.1 M KOH). That means that the efficiency of the OER performed in a low-electrolyte-concentration alkaline solution can be markedly enhanced by utilizing PAW in spite of the electrolyte concentration is reduced by 10% of magnitude compared to the DI water-based system. These interesting findings promise the PAW for the effective and green reactants and solvents.