Epoxides are essential chemical intermediates for the manufacturing of textiles, plastics, and pharmaceuticals. Existing routes, including both wet chemical and thermochemical approaches, have the drawbacks of large carbon dioxide footprints, stoichiometric waste products, and hazardous reagents. We have developed a route through which olefins can be epoxidized at ambient conditions, using water as the oxygen atom source. At the cathode, hydrogen is generated. Overall, this reaction provides a means by which the oxidation reaction can go towards generating a valuable product rather than generating oxygen which is simply vented in a conventional water electrolyzer. We have developed mechanistic understanding of how water is oxidized, providing means by which the selectivity for epoxidation can be rationally improved.