<p>Operating an electrolyzer (2) for generating hydrogen by decomposing water, comprises: storing waste heat produced within the electrolyzer in a heat transfer medium; supplying the heat transfer medium to a water treatment plant (10); and producing deionized water from raw water in the water treatment plant by the waste heat. An independent claim is also included for an electrolyzer system (1) for generating hydrogen and oxygen through electrolysis of water by the above mentioned method.</p>
