Recent revelations about the National Security Agency have brought a lot of attention to privacy concerns, on behalf of the agency as well as citizens. Amidst all the hubbub, news broke that a new NSA data center in Utah, its biggest yet, will consume enough energy to power 65,000 homes and gulp down 1.5 million gallons of water per day.
Data centers, which house computer data systems, are energy hogs that continue to fatten up thanks to our newfound love of cloud computing. The seemingly insatiable energy appetite of data centers has been well-documented: Facilities are often run at full power 24-7 regardless of demand, gobbling up two percent of the nation's electricity, and their backup generators are often powered by diesel - not the greenest of fuels.
But how data centers use water, and how much they use, is less well known.
There are nearly 3 million data centers in the US, ranging in size from several servers in an office closet to a 1.4 million square foot in-construction Facebook data center in Iowa. All of them use water, some directly, some indirectly. That is, many large data centers withdraw water directly to cool their servers, while nearly all use electricity generated at power plants - which rely on water for their own cooling needs - to power their servers and cooling systems.
For example, Amazon estimated back in 2009 that a 15 megawatt data center can require up to 360,000 gallons of water a day, leading one of the company's data center designers to admit that "water consumption (in data centers) is super embarrassing. It just doesn't feel responsible."
The good news is that water use at data centers does appear to be going down since that candid assessment. How do we know? A handy metric called Water Use Efficiency, or WUE, has been embraced by data center managers.
Here's just a tiny bit of math: WUE = Annual Water Usage (L)/IT Equipment Energy (kWh)
The resulting number will tell you how many liters of water per kilowatt hour are used onsite to operate the data center. If you want to get a more accurate WUE, and you should, then it's possible to add the amount of water required to generate the electricity used at the data center in question (The Green Grid provides all the figures and formulas needed).
The ideal WUE is of course 0, meaning that no water is used to operate the data center. But considering our current water-reliant energy system and the tendency of data centers to rely on water for direct cooling, don't expect to find that result any time soon.
Some large online companies are at least becoming more transparent about their water demands. Facebook, for example, has made its results public, posting real-time water and energy use updates for their data centers in North Carolina and Oregon. Ebay offers even more metrics for their data centers, including WUE, although on a quarterly basis.
Other data center heavy hitters are not so public with their WUE scores, but have been promoting their water efficiency work. Google is reducing water use at its data centers by using reclaimed wastewater. Both Microsoft and Yahoo are reducing their water use by installing air-cooling systems, which require just 1-3 percent of the water required for a traditional data center, although such cooling systems require more electricity to operate.
There are many ways for data centers, big and small, to reduce their water use, from raising the temperature and reducing humidity inside the centers to siting them in areas with optimum climate to using recycled water for cooling. All choices to reduce water use will impact energy use and carbon emissions, and vice-versa, in sometimes positive or negative ways. But remember that as more and more Americans rely on the internet to send emails, watch movies and pay bills - or in the NSA's case, keep an eye on all those digital transactions - we place even more strain on energy and water resources. It's just one more example of how the nexus of water and energy systems plays a direct role in our lives.