Water is the data centre impact communities ask about first and understand least, partly because the industry often answers with a single number when the real story is a journey: in as drinking water, around the loop a few times, partly into the sky, the concentrated remainder to the sewer under a trade waste agreement, carrying the chemistry that kept the system safe. Follow the litre and the assessment questions write themselves. The engineering endpoint, meanwhile, has already been named: the first zero-water designs are already running.
Why this matters
Water is one of the first questions communities ask about data centres and one of the hardest to answer from a headline consumption figure. The new NSW Data Centre Guidelines put water firmly into the assessment framework, setting design WUE targets, prioritising recycled water for water-intensive cooling and requiring drought resilience. But a WUE figure alone does not explain where the water comes from, where it goes or what it carries with it. Following a litre through the facility does.
A large evaporatively cooled facility can draw as much water as a small suburb and most public debate stops at that comparison. What the litre actually does between the meter and the sewer is better understood than almost any other industrial water use, because cooling water chemistry is seventy years old and thoroughly documented. The opacity is commercial, not technical: few operators publish what any water treatment engineer could describe from memory.
The journey
The litre arrives as makeup water, usually potable, sometimes bore water, increasingly recycled supply. It joins the condenser loop and heads for the cooling towers, where the system’s entire purpose is partial sacrifice: a fraction of the circulating water evaporates and that phase change is what carries the heat away. Evaporation is the principal consumptive loss: that water leaves the local liquid system as vapour. Most of the remainder eventually leaves as blowdown, with a much smaller share lost as drift.
What does not evaporate becomes more concentrated with every pass, because evaporation leaves the dissolved minerals behind. Operators track this as cycles of concentration: at four cycles the circulating water carries four times the dissolved solids of the incoming supply. Systems commonly run between two and four cycles and well-managed systems with suitable source water and treatment can reach six or more; push higher without that support and scale formation and biological risk climb steeply. To hold the balance, the system continuously bleeds off a share of the concentrated water as blowdown, typically carrying dissolved solids several times more concentrated than the incoming supply, with the actual level set by the source water chemistry and the cycles of concentration. Blowdown leaves through a trade waste agreement to the sewer, which is where the water story meets the regulatory system. A final small stream leaves as drift: fine airborne droplets carrying whatever the water carries, which is why drift eliminators and their maintenance matter more than their obscurity suggests.
Closed-loop chip cooling can change the journey dramatically, but a closed loop alone does not make a facility waterless. Direct-to-chip and immersion systems circulate a fixed charge of treated water or coolant indefinitely, yet the heat they collect still has to be rejected somewhere and that final stage may itself be evaporative. In genuinely zero-evaporation designs, the closed loop rejects heat through dry or mechanically assisted cooling without consuming water.
What is in the water
Four broad classes of additive keep an evaporative system safe and efficient. Scale inhibitors, led by phosphonates such as HEDP and PBTC with polymeric dispersants alongside, hold calcium carbonate in suspension instead of on heat exchange surfaces. Corrosion inhibitors protect the metals: azoles for copper, phosphates and molybdates for steel. Biocides are the environmentally consequential class, oxidising agents such as chlorine and bromine rotated with non-oxidising chemistries to prevent microbial resistance, with Legionella control the non-negotiable reason the dosing never stops. pH control and anti-foam agents complete the program. Modern sites increasingly meter all of this through automated dosing tied to real-time water chemistry rather than timers, which cuts both chemical consumption and risk.
Those treatment chemicals, their residuals and reaction products become part of the circulating water chemistry and much of that inventory leaves the system in the blowdown. Makeup volume tells us what the facility demands from the catchment or utility; blowdown quantity and chemistry tell us what it returns to the wastewater system. A credible assessment needs both and the blowdown half is the number applications least often state.
Can the litre be cleaned and used again?
Yes, and at a steadily falling cost. Side-stream filtration keeps circulating water cleaner and buys extra cycles of concentration, which is the cheapest recycling there is because it simply makes the first use last longer. Reverse osmosis can recover a substantial share of the blowdown for return to the towers, though recovery depends on the water chemistry and pretreatment and it leaves a concentrated brine that still has to be managed. Full zero-liquid-discharge, evaporating the brine to solids, is proven but energy-intensive and reserved for water-scarce sites. The more elegant move runs the journey backwards: source the makeup from recycled water in the first place, as Google has done with reclaimed municipal supply and Singapore does systematically with NEWater. Where recycled water infrastructure is available, recycled makeup plus higher cycles plus recovery on blowdown can cut potable demand dramatically using entirely conventional equipment; what is missing is usually the connection to a recycled water main, which is a planning question rather than an engineering one.
The innovations
The structural innovation is the same one reshaping heat and noise: move the cooling to the chip. One example is Microsoft, whose new designs adopted since August 2024 use a closed-loop, zero-evaporation architecture, with next-generation deployments at Phoenix in Arizona and Mount Pleasant in Wisconsin, where the first facility is now operational, and a claimed saving of more than 125 million litres per facility per year. Their fleet water use effectiveness had already fallen 39 per cent since 2021 to around 0.30 litres per kilowatt-hour. Around that headline sit quieter advances: smart dosing replacing scheduled chemical injection, non-chemical treatment using filtration, UV and electrochemical methods to shrink the biocide inventory, plus the water replenishment pledges of the major operators, which fund genuine catchment projects but should be read as offsetting alongside reduction, not instead of it.
The honest caveat belongs in every conversation about zero-water designs: closed loops and dry coolers trade water for electricity. Rejecting heat without evaporation generally takes more fan and compressor energy, though the size of the penalty depends on climate, coolant temperatures and the heat rejection design; Microsoft reports only a nominal energy increase for its zero-water architecture. Water use effectiveness and power use effectiveness still pull against each other at the margin and a facility quoting only its best number is telling half the story. In a dry inland catchment the trade is usually worth making; in a jurisdiction with abundant clean energy and stressed water it is worth mandating; either way the assessment needs both numbers.
What an assessor should ask
The new NSW Guidelines establish the performance outcome. The next question for an assessor is what evidence demonstrates it. Seven questions cover the journey. What is the full water balance, makeup, evaporation, blowdown and drift, at design load in the hottest week of the year, including peak daily demand? What cycles of concentration will the system run and what treatment supports that claim? What is the additive inventory and the blowdown quality entering trade waste, stated in the application rather than left to the sewer authority to discover? What is the Legionella management plan, since public health sits inside this system, not beside it? Was recycled makeup assessed and if refused, why, given the reference projects exist? What will be reported after commissioning and will actual operational WUE and PUE, potable and recycled volumes and peak demand be published against the design commitments made in the application? What is the source water hierarchy for normal operation and for drought and what happens to the facility’s demand when restrictions apply? None of these is onerous; all of them are answerable from the design documents of any competent applicant.
The bottom line
Water is where community concern and industry opacity meet head-on, yet the litre’s journey is the best understood story on the site. The chemistry is documented, the recycling technology is conventional, recycled makeup is proven and the zero-water endpoint is now a build program with dates rather than a research aspiration. What remains scarce is disclosure rather than technology and that is an assessment choice, not a technical constraint. The March 2026 national expectations put sustainable water use squarely inside the assessment conversation, New South Wales wrote water thresholds into its new framework this week and the Australian Government has announced that forthcoming standards will make water efficiency a legal obligation for large facilities. An assessment table that asks for the journey, not the summary number, will find that the industry already knows every answer; it has simply been waiting to be asked.
A topical commentary from the Digital Infrastructure Institute. Part of our series on what neighbours actually experience, alongside backup power, noise and heat. For plain-English community information on data centre water use, see our community information series.
Sources: Microsoft — next-generation datacenters consume zero water for cooling; DCD — Microsoft closed-loop, zero-water evaporation design; DCD — Google recycled water at Georgia data centre; DGTL Infra — data centre water usage guide