How to Read a Water Claim
In 2011, The Green Grid, the consortium that created power usage effectiveness, published a companion metric called water usage effectiveness, or WUE. In its simplest form, site WUE divides the annual water used on site for cooling and humidification by the energy delivered to the information technology equipment, and it is expressed in liters per kilowatt-hour. An international version was later published in 2022 by the International Organization for Standardization and the International Electrotechnical Commission, as the standard numbered 30134-9. Microsoft, in its December 2024 announcement, reported a WUE of 0.30 liters per kilowatt-hour for its most recent fiscal year, down from 0.49 in 2021. Numbers like these are now common in corporate reporting. Reading them well takes a few habits.
The first habit is to ask which water. Withdrawal counts all water taken in, including water returned to a sewer or river after use. Consumption counts water that does not return, chiefly what evaporates. A company can report either or both, and they can differ greatly. Withdrawal matters to a local utility that must supply the peak; consumption matters to a watershed that loses the water. When a figure is quoted without saying which, it is unfinished.
The second habit is to ask which boundary. Site WUE counts water used at the data center. The Green Grid also defined a source version that adds the water consumed in generating the electricity. The Lawrence Berkeley National Laboratory report of December 2024 showed why this matters, estimating indirect water use tied to data center electricity at more than ten times the direct on-site figure for 2023. A facility with a site WUE near zero is not a facility with no water footprint. It is one that has moved its footprint to the grid, which may be the right choice, but it should be described as such.
The third habit is to watch the denominator. Because WUE divides by information technology energy, a fleet that grows quickly can report a falling WUE while its total water use rises. Google's annual environmental reports illustrate the value of reading both. Google publishes water figures at the level of individual data center campuses, including large sites such as Council Bluffs, Iowa, which lets readers see absolute volumes rather than only ratios. Its reports have shown total water consumption rising as the business grew. A ratio describes efficiency. A volume describes impact.
The fourth habit is to separate operations from offsets. In September 2021, Google set a goal to replenish, on average, 120 percent of the fresh water its offices and data centers consume by 2030. In 2021, Meta, then still called Facebook, set a goal to be water positive by 2030, meaning it aims to restore more water than it consumes, with a focus on stressed watersheds. Replenishment projects, such as restoring wetlands or fixing leaking irrigation systems, can do real good, but they often take place in a different location from the data center that consumed the water. A replenishment claim and a consumption claim answer different questions, and neither substitutes for the other.
The fifth habit is to ask about the kind of water and the kind of basin. Some operators use reclaimed wastewater or non-potable sources for cooling, which reduces competition with drinking supply. Google has said it would pursue such alternatives. The same number of liters means something different in a region with abundant surface water than in one with depleted aquifers. Public water stress indicators, such as those published by the World Resources Institute in its Aqueduct tool, give a starting point for that context.
Put these habits together and a single sentence in a sustainability report expands into a set of questions. Is this withdrawal or consumption? Site or source? A ratio or a total? Direct reduction or replenishment elsewhere? Drinking water or reclaimed? Stressed basin or not? Faraday's read is that the best disclosures answer most of these without being asked, and that the absence of an answer usually tells you which way it would have gone.
The last point is the one this whole course has been building toward. Heat is the constant, set by the electricity the computers draw. Water and energy are the two currencies a building can spend to get rid of it, and every design spends some of each. Evaporation saves energy and spends water. Dry cooling saves water and spends energy. Warm-water liquid cooling narrows the gap by letting heat leave at a higher temperature, which is why the plumbing at the chip turns out to matter for the water table. When you next read a claim about a data center's water, look for the energy on the other side of the ledger.