Cooling demand in data centers is rising, and data center operators are playing a balancing actAs rack and workloads increase with increased artificial intelligence (AI) functions and services, business goals expand, and data centers transition to scalable technologies, facility operators are finding techniques and methods to maximize and stretch water utilization.
What is water usage effectiveness (WUE)?
As operators find efficient cooling designs and innovations, one tested metric and approach involves tracking water usage effectiveness (WUE). WUE measures how efficiently a data center uses water for cooling. Introduced by The Green Grid, it has become a key metric as AI drives rack densities up to 130 kW. Berkeley Lab’s 2024 US Data Center Energy Usage Report furthered this uptick as data showed that average WUE across U.S. data centers rose from 0.36 kW to 0.45 kW–0.48 kW as hyperscale and colocation sites expanded.
Figure 1. Annual average site WUE across U.S. data centers (Berkeley Lab 2024 US Data Center Energy Usage Report)
Tracking WUE helps teams identify where water is being wasted, optimize cooling strategies, and make informed decisions about infrastructure upgrades. For organizations, monitoring usage and controlling it can translate to the infrastructure’s lower utility spend, fewer regulatory headaches, and stronger long-term resilience.
The equation below computes how much water a data center uses to support each kilowatt-hour of IT energy. As a rule of thumb, a lower result indicates a more efficient water utilization.
Tracking WUE sets the baseline. Improving it often starts with how cooling systems manage water reuse, especially through the cycle of concentration.
Cycle of concentration: a lever for better WUE
Balancing the cycle of concentration (CoC)—the ratio of solid impurities in reused and recirculated water in comparison with makeup water discharged and concentrated via evaporation—can reduce makeup water needs by 20%, translating to cost savings. Achieving a balanced CoC requires chemical treatment to control scaling and biofouling, which also protects downstream heat exchangers. Variable frequency drives (VFDs) on tower fans and pumps cut energy use by matching output to demand, indirectly lowering water use by reducing evaporation rates. These measures directly improve WUE without requiring wholesale changes to the cooling loop.
Key strategies to optimize data center water usage
While water-based cooling remains effective, its role must be weighed against emerging alternatives.
- Closed-loop liquid cooling systems: Closed-loop systems recirculate water through heat exchangers, cutting water withdrawal by 50% to 70%, depending on climate and load. This design reduces chemical treatment, simplifies monitoring, and maintains consistent water quality. But it also requires careful planning to handle heat rejection in high-density environments, especially in areas with water availability constraints.
- Hybrid cooling systems: Hybrid systems combine air and liquid cooling to improve thermal performance while reducing water use. These systems often operate in dry mode for most of the year, using ambient air to reject heat and keeping WUE near zero. They work well in moderate climates but may struggle to maintain efficiency in extreme conditions or during peak loads.
- Refrigerants as a practical alternative: Water-based cooling has limits, especially in regions with evolving water usage regulations. Refrigerant-based systems eliminate water use, simplify operations, and handle high-density workloads efficiently. For facilities facing these challenges, refrigerants offer a scalable, low-maintenance solution. However, refrigerants can increase energy consumption, which may impact operating costs. Despite this, they remain a reliable alternative for facilities facing water constraints.
Monitoring and real-time optimization
Cooling efficiency depends on more than hardware—it requires tight monitoring control and real-time visibility. Sensors tracking temperature changes, humidity, and flow feed data into platforms that adjust setpoints automatically based on load and climate conditions. Systems like Vertiv™ Liebert® iCOM™-S analyze hundreds of data points to fine-tune water temperatures, fan speeds, and cooling output. This reduces swings in WUE, flags anomalies early, and supports predictive maintenance. For operators, this also means fewer surprises, better resource use, and more stable performance across changing workloads.
Scaling cooling without scaling water demand
Applying WUE-focused strategies, like closed-loop systems, hybrid cooling, and automated controls, can support high-density workloads while keeping water consumption stable. This approach helps operators manage resource use more precisely, reduce operating costs, and stay aligned with environmental standards.
Learn how Vertiv applies these strategies in real-world data centers. Explore Vertiv’s 2024 Responsible Business Report for more insights on water efficiency.
