The "Eurora" supercomputer that was just fired up in Italy may not be large, but it has taken the lead in energy efficiency over designs from big HPC vendors like Cray and IBM. The new machine was built by Eurotech, a server maker with HPC expertise that is based on Amaro, Italy, in conjunction with graphics chip and GPU …
Ok, what can one throw away to use less energy then?
I know that "3-8-12 NEVAR FORGET" (i.e. if you erase bits in a classical machine, you must transform a minimum of energy into heat, see here) but there is still some way until we reach that limit. So... asynchronous logic? Supercooled circuits? Josephson junctions/Quiterons? Optical interconnects? Definitely new industries are needed.
OK, so the Eurora needs less electriciy, but how much tap water does it consume?