Electricity extraction from water by twin electrodes, mediated by oxygen molecules, that we call Oxhydroelectric Effect, is reported. The extremely simple components of this experimental system are: two platinum (Pt) wire electrodes, a saturated solution of potassium carbonate (K2CO3) in water (H2O) (with pH >10) as electrolyte, and a film of hydrophilic material (Nafion®). A dc power of the order of hundredths of nW was measured for days through a resistor connected to the twin Pt electrodes. The addition of a very small amount of hydrogen peroxide (H2O2) to the electrolyte (water-potassium carbonate solution with only 0.004% H2O2), as a source of oxygen, determines an immediate dc power jump, more than two orders of magnitude high, lasting for days. The Oxhydroelectric Effect opens the way to a completely new paradigm in what concern low-cost electrical energy generating systems, with a tremendously wide range of possible applications.