Data centre water use is one multiplication, but the answer moves by a factor of thirty with the cooling design, and the water saved on site is partly spent again at the power station.
Annual water use is the site's water usage effectiveness (WUE, litres per kWh of IT energy) times its IT energy. An illustrative 100 MW data centre running at 75 per cent utilisation consumes 657 million kWh of IT energy a year, so at an illustrative WUE of 1.8 with evaporative cooling it uses about 1,182.6 million litres a year, 312 million US gallons or 3.24 million litres a day. The same campus on closed-loop cooling, at an illustrative WUE of 0.05, uses 32.9 million litres, but buys 98,550 MWh more electricity to do it.
Worked in full in The Data Center Development Handbook by Julian R. Sterling, with every figure reproduced in a free workbook.See the book on Amazon →
Water has moved from a footnote to a permitting question in many data centre markets, and the figure quoted in local hearings is often either the full design capacity or a single headline WUE with no load attached. Both can be off by a wide margin. The levels used below are illustrative assumptions chosen to show the mechanics, not benchmarks for any facility or market. The arithmetic below separates the three things that drive the number: the IT energy, the cooling design, and the water embedded in the power.
| Input | Value |
|---|---|
| Critical IT capacity | 100 MW |
| Average IT utilisation | 75% |
| Hours a year | 8,760 |
| WUE: evaporative / hybrid / closed loop (L per IT kWh) | 1.80 / 0.50 / 0.05 |
| PUE: evaporative / hybrid / closed loop | 1.20 / 1.27 / 1.35 |
| Water intensity of grid power (L per kWh) | 1.5 |
| Power price, per MWh | 80.00 |
| Water and sewer price, per m³ | 3.00 |
IT energy (kWh) = IT MW × utilisation × 8,760 × 1,000
Site water (litres) = WUE × IT energy
Indirect water = grid water intensity × IT energy × PUE
In Excel: =WUE*IT_MW*Utilisation*8760*1000 for litres a year.
| Design | Site water, million L | Per day, m³ | Facility energy, MWh | Indirect water, million L | Total, million L |
|---|---|---|---|---|---|
| Evaporative cooling | 1,182.6 | 3,240 | 788,400 | 1,182.6 | 2,365.2 |
| Hybrid (evaporative in summer) | 328.5 | 900 | 834,390 | 1,251.6 | 1,580.1 |
| Closed loop, air or liquid | 32.9 | 90 | 886,950 | 1,330.4 | 1,363.3 |
On site, the closed loop uses about one thirty-sixth of the water of the evaporative design. Across the whole footprint the saving is 1,001.9 million litres, 42 per cent, because the chillers that replace evaporation run on electricity. Where the grid is thermal and water-stressed, that indirect line belongs in the comparison; where it is wind and solar, much less so.
What the water saving costs. Closed loop instead of evaporative saves 1,149,750 m³ of site water a year and adds 98,550 MWh of power. At 80.00 per MWh that is 7,884,000 a year, or 6.86 per m³ saved, against 3,449,250 of avoided water bills at 3.00 per m³. A hybrid design saves 854.1 million litres for 45,990 MWh, about 4.31 per m³. Whether either is worth it depends on the water tariff, the permit, and what a lost megawatt of leasable capacity is worth, since a higher PUE also shrinks the IT load a fixed grid connection can carry.
| WUE (L/kWh) | 50% utilisation | 75% utilisation | 90% utilisation |
|---|---|---|---|
| 0.2 | 87.6 | 131.4 | 157.7 |
| 0.5 | 219.0 | 328.5 | 394.2 |
| 1.0 | 438.0 | 657.0 | 788.4 |
| 1.8 | 788.4 | 1,182.6 | 1,419.1 |
Utilisation moves the answer far less than the cooling design, which spans a factor of thirty-six, but it is the input most often left out. A new AI campus that fills quickly and runs dense training loads near 90 per cent will use 20 per cent more water than the same building at 75 per cent, and WUE itself rises in hot, dry summers, which is when water is scarcest.
For a developer the question usually arrives earlier than the operating figures. The water utility wants a peak daily demand to size the connection, the planning authority wants an annual figure and a drought plan, and the end tenant wants a WUE commitment in the lease. All three come from the same multiplication run on different loads: peak summer days, the average year, and a contractual ceiling. Running them together, before the cooling design is fixed, is what keeps a water constraint from surfacing after the land is bought.
The usual error is to multiply WUE by the utility connection at full load: 1.8 × 100 MW × 1.20 × 8,760 hours gives 1,892.2 million litres, 60 per cent too high. WUE is defined per kWh of IT energy, not facility energy, and no campus runs at 100 per cent of its capacity all year. Even at full IT load the answer is 1,576.8 million litres. The opposite error, quoting a closed-loop WUE as if the campus used no water at all, ignores the 1,330.4 million litres embedded in its power.
The WUE, PUE and grid water figures here are illustrative; actual values vary widely with climate, cooling plant and generation mix, so replace them with the design team's and the utility's figures. Water use is WUE times IT energy, and IT energy is capacity times utilisation times hours. For an illustrative 100 MW campus at 75 per cent that is about 1.18 billion litres a year with evaporative cooling and 32.9 million with a closed loop, and the saving costs about 6.86 per m³ in extra power. The electricity side of the same campus is worked in how much electricity a 100 MW data centre uses, and the free workbook for this book carries the full development underwrite.
Water usage effectiveness is the site's annual water consumption in litres divided by the IT equipment's energy in kWh. It measures cooling water only, not the water used to generate the electricity. In the illustrative case, with assumed values rather than measured ones, an evaporative design at 1.8 L/kWh uses 1,182.6 million litres a year on 657 million kWh of IT energy; a closed-loop design at 0.05 uses 32.9 million.
Divide the annual figure by 365. The illustrative 100 MW campus at 75 per cent utilisation uses about 3.24 million litres a day with evaporative cooling, 0.90 million with hybrid cooling and 0.09 million with a closed loop. Peak summer days run well above the average for evaporative designs, which is the figure a water utility will size its connection to.
No. It removes most on-site water but raises PUE, so the facility draws more power, and power generation uses water. At an illustrative 1.5 litres per kWh of grid water intensity, the closed-loop campus still accounts for 1,363.3 million litres a year in total, against 2,365.2 million for evaporative cooling: a 42 per cent saving, not 97.
This article is one calculation from The Data Center Development Handbook. The book takes the same case from first principles to the decision, chapter by chapter, and every figure it prints is a live formula in the free companion workbooks.
Get the book on Amazon →Free companion files
Also on Amazon UK · Amazon Germany · Amazon France · Amazon Canada
Reading guide: infrastructure, data centres and energy → · All 453 articles →
If this book helped, or didn’t, a few lines on Amazon are worth more than they look: they are what the next reader goes on. Write a review. The workbook stays free either way.