Every watt a data center draws ends up as heat, and something has to carry that heat away. The choice of cooling system decides how much electricity the building uses on top of its servers, how much water it consumes, and how much of that water is used on site or at a power plant. As AI racks get denser, operators are moving to liquid cooling, and some now advertise "zero-water" designs. This article explains the main cooling approaches, what Microsoft and Google say about the trade-offs, and how to read a zero-water claim. For the electricity side of the picture, see what US official data shows about data center electricity use; for the hardware, see GPU vs TPU accelerators compared.
Why data centers need cooling at all
Microsoft puts it simply: servers produce heat and "must stay at the right temperature, which requires cooling."[3] Google says the same in its own words, that data centers generate heat and need to be cooled to operate, and describes its decisions as "balancing the trade-offs between using energy and water for cooling."[5]
That trade-off is the whole subject. Water can carry heat away cheaply because evaporating it absorbs a lot of energy, so evaporative cooling needs less electricity. Removing the water means replacing evaporation with mechanical cooling, which draws power. Neither company claims a free option.
The main approaches, as the sources describe them
| Approach | How it works, per the source | Water | Energy note from the source | Source |
|---|---|---|---|---|
| Outside-air cooling with evaporative assist | Outside air cools the building; water is added only when it is hot. Microsoft says this has been used across its fleet since 2008 and uses water only when outside temperatures exceed 85°F (29.4°C) | Used only in hot periods; water cycles 2 to 5 times and a portion evaporates | Microsoft says outside air alone can cool many data centers below that temperature | Microsoft [2][3] |
| Cooling towers | Evaporate water through the year, according to Microsoft's definitions | Evaporative, year-round | Not quantified in the pages we read | Microsoft [2] |
| Water-cooled, using sourced or recycled water | Google says options include air cooling, water cooling, refrigerants or a combination, chosen per site | Varies; Google reports reclaimed or non-potable water at more than 25% of campuses (2022) | Google: water-cooled data centers use about 10% less energy than many air-cooled ones | Google [4] |
| Closed-loop, chip-level liquid cooling | Water recirculates through a closed loop with no evaporation; Microsoft's 2024 AI design | Filled once; Microsoft says zero water consumed for cooling during operation | Microsoft says PUE rises, offset in part by warmer water temperatures and economizing chillers; it calls the energy increase nominal and gives no figure | Microsoft [1] |
Two details are worth keeping. First, Google's 10% figure compares water-cooled sites with "many" air-cooled ones in a 2022 post, not a measured fleet average today.[4] Second, Microsoft's page for the 2024 design uses the term "chip-level cooling," not direct-to-chip; the June 2026 post describes the same design as recirculating, closed-loop, direct-to-chip cooling.[1][2]
What the numbers say, and what they do not
Microsoft's June 2026 post says its average water usage effectiveness (WUE) fell from 2.3 to 0.27 litres per kilowatt-hour in 2025, and that about 90% of its 2025 owned fleet operates on "low- to zero-water" cooling systems.[2] The post does not say how much of that is specifically closed-loop. The December 2024 post states a different figure, a "FY 2024 global average withdrawal WUE of 0.30 L/kWh", and uses it to estimate that the new design avoids more than 125 million litres of water per year per data center.[1] We do not know whether the 0.30 and 0.27 figures use the same boundaries, so we do not compare them directly. The 125 million litre figure is an estimate that multiplies a fleet average by the data center's load, not a measurement at one site.
Google's most recent per-site figures that we found are from 2021: an average data center used about 450,000 gallons per day, and the global fleet about 4.3 billion gallons.[4] They are five years old. Google's current water page gives no consumption totals; it says Google reports annual water use for its data center locations elsewhere, which we did not open, and it describes a goal to replenish more freshwater than it consumes across data centers and offices by 2030, which is a target, not a result.[5]
How AI hardware changes the picture
NVIDIA describes the GB200 NVL72 as connecting 36 Grace CPUs and 72 Blackwell GPUs in "a rack-scale, liquid-cooled design," and says liquid cooling increases compute density and reduces floor space.[6] The same page says liquid-cooled racks reduce water consumption and carbon footprint, but gives no figure, and it states no rack power draw. Our reading is that dense racks are the reason liquid cooling is spreading, because moving that much heat with air alone requires far more space and airflow. That is an interpretation. The sources we opened do not quantify it.
Five checks for a zero-water claim
- What is the boundary? Microsoft's claim covers "cooling during operations." Water is still used for restrooms and kitchens, and the loop needs an initial fill.[1]
- Is it a design or a fleet? The 2024 design applies to new builds. Microsoft says its pilots in Phoenix and Mt. Pleasant, Wisconsin come in 2026, new sites online from late 2027, and that its existing fleet still mixes air-cooled and water-cooled systems.[1]
- What happened to the energy? Microsoft says PUE increases. Ask for the PUE and the annual energy change, not only the water saved.
- Where does the electricity come from? Power plants also use water. None of the pages we read quantifies this, so a site-level water figure may not capture the whole picture. Treat that as an open question.
- Is the number measured or modelled? Withdrawal versus consumption, fleet average versus site, and the year all change the figure. Check the footnote.
Limitations of this article
We read company pages only. We could not open the Lawrence Berkeley National Laboratory data center report, which the US Department of Energy cited in its December 2024 announcement, so no independent estimate of data center water use appears here. We ran no measurements. Microsoft's local water-use page carries no date, so we list the retrieval date, 1 November 2026. We will add a dated update when an independent source is opened and verified.
