The effect of water on CO2 hydrogenation to produce higher alcohols (C2–C4) was studied. Pt/Co3O4, which had not been used previously for this reaction, was applied as the heterogeneous catalyst. It was found that water and the catalyst had an excellent synergistic effect for promoting the reaction. High selectivity of C2–C4 alcohols could be achieved at 140 °C (especially with DMI (1,3‐dimethyl‐2‐imidazolidinone) as co‐solvent), which is a much lower temperature than reported previously. The catalyst could be reused at least five times without reducing the activity and selectivity. D2O and 13CH3OH labeling experiments indicated that water involved in the reaction and promoted the reaction kinetically, and ethanol was formed via CH3OH as an intermediate. Water can enhance the synthesis of C2–C4 alcohols (C2+OH) from CO2 hydrogenation over Pt/Co3O4 significantly. The alcohols can be produced at a lower temperature with satisfactory activity and selectivity. DMI=1,3‐dimethyl‐2‐imidazolidinone.