There are several new sustainability measures we will have to learn if we want to improve our 'green' datacenter.
PUE - Power Usage Effectiveness
ERE - Energy Reuse Effectiveness
WUE - Water Usage Efficiency
CUE - Carbon Usage Effectiveness
ERE is related to the reclamation of heat to use it as energy again.
WUE covers water usage in evaporative cooling measures. This tends to be site-specific.
CUE This one measures the use of carbon both in the running of the on site systems and in the electicity purchase to run the rest of the datacenter and offices.
There is a great deal more to think about now as we plan or upgrade of datacenters.