Data Centers Consume 80-215% More Water When Power Generation Is Included

Data centers have made headlines for the large amount of water they use to cool their computer chips. But data centers also typically trigger major off-site water consumption associated with electric power generation. We must add together both on-site and off-site water use to get the whole water use picture. 

Whether it is on-site or off-site, water use generally includes two components: water withdrawal and water consumption. 

Water withdrawal refers to the amount of water removed from its source for a certain use. For instance, pumping water out of a river is a form of water withdrawal. Often some or most of the withdrawn water is discharged back into the river, with changes such as elevated temperature or reduced oxygen. 

Water consumption is the loss of withdrawn water to the immediate water environment by way of processes such as evaporation. Water that is evaporated by a data center doesn’t return to the local watershed, and thus alters the environment in a qualitatively different way from other processes such as withdrawal or pollution. While both water withdrawal and water consumption impact the environment, this analysis focuses only on consumptive water use to better compare direct and indirect water use of data centers. Also, while water use for data centers varies from site to site, this analysis draws general conclusions based on typical technologies.

Direct Water Consumption

First, we’ll consider water consumed at the physical location of the data center. Many large tech companies report their annual on-site water use, but not all companies measure water use in the same way. Google’s reports are clearer than those of its competitors and provide a reasonable picture, for this analysis, of total water and energy consumed across its entire data center portfolio. Below is the average Google data center’s direct water consumption.

While there is likely a wide range of water consumption rates among each individual data center within Google’s portfolio due to differing site-specific traits, we can use Google’s overall data to derive an average portfolio-wide water consumption rate and apply it to a hypothetical data center. For example, a 100 MW data center operating at 90% of the hours in a year would directly consume almost 196 million gallons of water. 

This metric, however, only tells part of the story. Data centers require around-the-clock power generation, which, in turn, typically requires cooling water. We turn now to an estimate of the indirect water consumption at the power plants supplying these data centers in order to get the full picture of data center water usage.

Indirect Water Consumption

Most of the electricity sold in the United States is generated through a process that uses heat to convert water to steam or expand gas (or both) to drive a turbine. The heat comes from one of three kinds of fuel: coal, nuclear, or “natural” gas. All of these heat-driven processes require cooling systems that typically use water. 

Most large data centers buy power from their local electric utility. To get an idea of how much water it takes to provide energy to a data center located in the Southeast, we can look at the average rates of water consumption for the most common types of baseload power generation in the region. Although coal remains a significant portion of the fuel mix for some Southeast utilities, the role of coal in electricity generation in the region has declined over the past few decades, so we focus on the natural gas combined-cycle plants (“CCs”) and nuclear plants that are the primary generation resources in the region. These plants can have various configurations for cooling, but we focus on the most common, which is a cooling tower.

As demonstrated below, a typical CC uses 197 gallons for each MWh of electricity that it generates. The power required to operate a 100 MW data center served by a typical CC would thus consume 155 million gallons of water per year. The data center’s offsite water use for power generation with natural gas thus adds an additional ~80% to the onsite water use to cool the data center. 

Nuclear energy uses far more water than gas: 536 gallons per MWh of electricity. A hypothetical 100 MW data center supplied by nuclear energy would thus use 422 million gallons of water for power generation—more than twice as much water (215%) as the data center consumes directly onsite.

Data centers are powered by whatever mix of power plants the local electric utility uses. Since wind and solar power use no cooling water, to the degree the electric utility uses renewable energy, it reduces the average water use for power. But the sudden massive growth in data centers is spurring a rush all over the Southeast to build gas-fired power plants and a renewed interest in new nuclear plants. 

Potential Shifts in Indirect Water Consumption

Increasing renewable energy generation would avoid some of the massive data center water footprint. Also, some of the new gas-fired power plants use “dry” cooling systems that use significantly less water than water-cooled plants. For the foreseeable future, however, even these more efficient new plants will add incremental water use to an existing power system that is heavily reliant on water-intensive cooling systems (Form EIA-923). And any new nuclear coming online will almost certainly be using wet cooling systems, most likely with a cooling tower configuration consuming water at a rate around 536 gal/MWh. 

Conclusion

The core purpose of this article is to estimate that a typical data center can trigger offsite water usage for power generation that is about 80%-215% of its on-site water usage, depending on whether the local electric utility’s power mix is more reliant on gas-fired power plants or nuclear energy. Looking into the near future, the Trump Administration’s vigorous efforts to spur data center and power plant construction almost guarantee a continuation of the enormous water usage the typical data center already triggers. And this will only be amplified to the degree electric utilities follow through with plans to build new nuclear units. Unfortunately, the Trump administration is also working to kill and delay renewable energy projects that might offset some of this increased water usage. All of these factors should be considered when local governments evaluate data center development under the current water and energy policy environment.