A typical data center drains an Olympic-sized swimming pool every two days. Is that a problem?
Gold has increased seven percent in value since the mid-1990s. Real estate jumped nine percent. Water, not normally considered an investment, beat both, increasing 10 to 12 percent.
Now add shortages to the ever-increasing cost of water, and data centers known for using huge quantities of water are being looked at with a certain amount of disdain. Is this justified?
Evaporation and blow-down
James Hamilton, vice president and distinguished engineer at Amazon Web Services, saw the problem coming in 2009. In his Data Center Efficiency Summit presentation, Hamilton mentioned that conservation is not just about power. It’s about water consumption; in particular, evaporation and blow-down losses.
Evaporation and blow-down losses are by-products of a common method used to cool data centers, where hot exhaust air exiting from electronic equipment is cooled by passing it through an air/liquid heat exchanger. The liquid coolant also passing through the exchanger picks up the heat on its way to cooling towers, another form of heat exchanger that uses water evaporation to remove heat from the liquid coolant.
Besides losing water through evaporation, data centers using cooling towers also lose water during blow-down. The liquid portion of the cooling system and cooling towers build up sediment; cooling efficiency suffers if this is not removed.
So, on a regular basis, the system purges a certain amount of water holding the sediment. These two operations are the reasons why data centers use as much water as they do.
The Green Grid, a source of the power usage effectiveness (PUE) metric, launched a measure of water use called WUE (water usage effectiveness) in 2010 and, although Facebook reported a WUE figure in 2012 it has not been used widely (see box below).
The issue of water use seemed to go quiet, until Drew Fitzgerald penned Data Centers and Hidden Water for the Wall Street Journal. Then things got interesting.
In the article, Fitzgerald focused data on one US state – California – which he obtained from 451 Research. California is home to 800 data centers (more than any other state), and each year they consume enough water to fill 158,000 Olympic-size swimming pools. And, lest we forget, California is in its fourth year of a severe statewide water shortage.
Hamilton recently acknowledged Fitzgerald’s WSJ article on his Perspectives blog and reiterated his stance, saying: “Water consumption is the next big natural resource issue for data centers after power. I think it’s still true today and expect that water consumption will continue to need to be managed carefully by all data center operators.”
Data centers use 0.7 percent of California’s water. Agriculture uses 60.7 percent
Using swimming pools as an analogy may be a nice visual, but it does not equate well when trying to determine just what it all means. So, the first step becomes determining how much water is needed to fill 158,000 Olympic-size pools. Thankfully, Marc Andreessen figured that out – 104,280,000,000 gallons.
Rather than just accept Fitzgerald’s amount at face value, let’s compare his total to what Hamilton mentioned in his presentation – that a typical (15MW) data center uses 360,000 gallons of water per day. If one takes a second and reflects on that number, it is somewhat mind-boggling that 360,000 gallons of water (half the water in an Olympic-size swimming pool) pass through a data center each day.
Time for some simple math: multiply 360,000 gallons by 800 (the number of data centers), then multiply the results by 365 (days in a year). The answer is 105,120,000,000 gallons – close enough (you will see why in a second).
Overall impact of data centers
Now let’s try to gauge the impact that data centers have on the overall water usage in the state. Information needed to help determine that can be found in the 2014 US Geological Survey’s (USGS) Water Use Estimates for California. The report states: “In 2010, Californians withdrew an estimate of 38 billion gallons per day.” Just to get an idea of how much that is, the USGS’s report states: “Water use in the US in 2010 was estimated to be about 355 billion gallons per day.”
How much of that is used by data centers? We need to divide 104,280,000,000 gallons by 365 days to get the amount of water used each day by all 800 California data centers. That number is 285,698,630 gallons. Next, let’s figure out the percentage: dividing 285,698,630 gallons by 38 billion gallons comes to 0.7 percent – and Hamilton’s statistics agree. It seems that California’s data centers use 0.7 percent of the water consumed in California.
How does that compare? To understand whether a bit less than one percent is significant or not when it comes to state-wide water usage requires us to find out who else uses the state’s water and how much. Referring back to the USGS’s California water usage report, we find that irrigation tops the list at 60.7 percent (23,056 million gallons per day), followed by thermo-electric power generation at 17.4 percent (6,601 million gallons per day).
swimming pool water drink left
What’s the problem?
One wonders, looking at those numbers, why Hamilton and others are so alarmed. Combined, all of California’s data centers only use one-fourth of one million gallons of water per day.
In the grand scheme of things data centers’ water usage is minor, but leaders in the industry are concerned. As well as Hamilton, others have spoken out, including Lisa Jackson (who led the US Environmental Protection Agency until 2013 and is now Apple’s environmental director), and Joe Kava, Google’s data center operations executive. They view wasted water as inefficient operation, bad for the environment, and ultimately bad for us. I suspect they would feel that way if the daily amount was even less than it is.
“This is an area (water conservation) where the industry will keep innovating,” says Hamilton, “and I expect to see results along the line as we have seen with power, where compute usage has gone up dramatically but power consumption has not.”
In less than a decade data center operators have addressed the power issue and taken responsibility for how much electricity they use, with most of the major data center operations moving towards using 100 percent renewable power.
In another 10 years, we may see similar changes around water use.
The WUE metric
Following the success of its power usage effectiveness (PUE) metric, in 2010 The Green Grid defined a metric to help discuss the amount of water used by data centers.
WUE, or water usage effectiveness, is measured in liters/kWh and is defined as the site’s annual water usage, divided by its IT equipment energy. The WUE metric should include both water used on site, and water used off site; for instance, in producing the electricity used by the data center.
WUE has not been widely used in the industry, and is only rarely quoted, but water use has become a more significant factor for data centers, leading to calls to find a way to incorporate water into the PUE metric.