Research Note: Data Center Resource Flow and Metric Dictionary

Research Note: Data Center Resource Flow and Metric Dictionary

Physical model

Electricity enters a data center through grid or on-site supply. Power-conversion and distribution equipment conditions it for servers, storage, and network equipment. Computing turns almost all of that electrical work into heat. Fans, pumps, chillers, cooling towers, dry coolers, or liquid loops move the heat to an outdoor sink. Lighting, controls, security, fire protection, and other facility systems add smaller loads.

Water can appear at several boundaries. A facility may consume water directly through evaporative heat rejection, use water without consuming all of it, receive reclaimed rather than potable supply, discharge water to a sewer, or use little on-site water while drawing electricity from generation that has its own water footprint. Direct facility water and electricity-related source water are different quantities.

AI training and inference both run on computing equipment. Their resource use depends on model architecture, hardware, precision, batch size, utilization, data movement, cooling, duration, and the number of requests or training runs. A universal multiplier against one web search hides more than it reveals.

Metric dictionary

The US Energy Information Administration explains the power and energy distinction. One megawatt sustained for one hour is one megawatt-hour. A 300 MW request is not the same statement as 300 MWh of annual consumption.

The Department of Energy design guide defines PUE as total annual facility energy divided by annual IT-equipment energy. It defines WUE as annual site water use divided by IT energy and discusses source WUE as an expanded boundary.

The US Geological Survey calls water removed from ground or surface sources a withdrawal. Consumptive use is the portion that does not return to local water bodies or groundwater, including evaporation and water incorporated into products.

The EPA water-reuse overview defines water reuse as treating and repurposing wastewater, stormwater, or another source for an appropriate beneficial use. Treatment requirements depend on the source and intended use.

Current national values

The 2024 LBNL report estimated 176 terawatt-hours of US data-center electricity use in 2023 and described facility infrastructure as about 30 percent of total data-center energy in that model year. It estimated 66 billion liters of direct site water use in 2023, with hyperscale and colocation facilities accounting for most of that total.

The report's modeled national average site WUE sat just above 0.36 liters per kilowatt-hour through 2023 and rose in its scenarios as facility mix and cooling changed. These are national modeled values. They cannot be assigned to a named facility without its own measurement record.

Editorial use

Every numerical claim should carry geography, time period, unit, denominator, operating or utilization assumption, facility boundary, water type, measured or modeled status, and source date.

PUE and WUE should be written as partial indicators. A lower PUE can coexist with higher total electricity when IT load grows. Lower on-site water use can coexist with higher energy demand. Reclaimed water can reduce pressure on potable supply while still requiring treatment, infrastructure, and a local allocation decision.