Data centres – warehouses where thousands of computers drive our online activities as well as an increasing amount of data computation and storage – are heavy electricity users. This paper proposes reusing the energy after the computers have transformed the electricity into waste heat. Two novel strategies are presented, commodity dehydration and increased work efficiency for ocean thermal energy conversion (OTEC) technology. We argue that data centre waste heat use is possible both in cold and warm nations, but that strategies to use the heat efficiently must be case-dependent. With the prospects of saving billions of dollars and many tons of carbon emissions, as well as bringing societal gains globally, it is concluded that few, if any, other energy savings can be this advantageous for the data centre industry.