When Microsoft's Quincy data center opened, I was able to get a tour of the data center. One of the questions I asked is how much water does the data center use. I asked the data center operations staff, they didn't know. I asked the data center design team, they didn't know either. And, a response was why do you want to know? Because I think you use lots of water, and it is an issue in a green data center.
When I went back out to the data center a few months later, the data center operation team said they are storing blow-down water in tanks, and they have 6 months before the tanks fill up. This problem was not unique to Microsoft as other data center operators had blow-down water that cannot be put into the waste stream.
A water treatment plant was built to reduce the environmental impact. And now, Microsoft has put a plan in place to transfer the water treatment plant to the City of Quincy.
Microsoft’s Data Center Takes Fresh Approach On Water Reuse13 Oct 2011 10:00 AM
Google's Joe Kava discussed water use in data centers in its 2009 data center summit. Joe's presentation on water start at the 9:20 mark.
A green data center has smart water use in addition to efficient power and cooling systems.