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Municipal recycled water for AI data-centre cooling: a Middle East & UAE design guide

Writer: Mark Cullens
Mark Cullens
2 days ago
10 min read


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Municipal recycled water can replace part or all of the potable make-up used by evaporative cooling systems at AI data centres, provided the project treats the utility supply, on-site treatment plant and cooling system as one controlled water circuit. Suitability depends on more than the average quality stated by the supplier. The design must cover feed-water variation, treatment recovery, storage, blending, cooling-tower concentration, biological control, discharge and the response to an interruption or off-spec delivery.


The opportunity is strongest at sites with cooling towers, evaporative condensers or hybrid heat rejection. Closed technology-cooling loops normally require small volumes of tightly controlled fill water and should remain hydraulically isolated from recycled water. Dry heat rejection may consume little routine process water, so a dedicated recycled-water connection may not be justified.


The decisive question is therefore not whether recycled water is available. It is whether the complete utility-to-tower arrangement can protect cooling capacity, public health and environmental compliance through normal, peak and abnormal conditions.


Where the project needs a repeatable packaged solution, the DC-MU make-up conditioning module converts these requirements into defined battery limits, controls and guarantees; campuses treating their own wastewater should also review the DC-RW reuse guide.


For network availability, approvals and application choices specific to the Emirates, see the UAE reclaimed-water applications guide.


1. Define the application before specifying treatment

Recycled water should be assigned to a clearly defined duty. For most AI data centres, the main opportunity is make-up to an open evaporative heat-rejection system. The recycled stream replaces evaporation, blowdown, drift and other losses, while a separate closed facility-water loop transports heat from the IT cooling equipment to the heat-rejection plant.


This distinction matters. Direct-to-chip cold plates, coolant distribution units and immersion systems may operate with carefully controlled fluids, but they do not necessarily consume water. Routine site consumption is governed by the final heat-rejection method. The project should therefore confirm the cooling architecture before estimating recycled-water demand.


The design basis should identify every intended use: cooling-tower make-up, initial filling, cleaning, irrigation, toilet flushing or other non-potable services. Each use needs its own quality, pressure and availability requirement. Combining all duties into a single high-quality treatment train can waste energy and chemicals; serving sensitive equipment from a general recycled-water network can create avoidable risk.


The source also needs a clear name. Terms such as treated sewage effluent, reclaimed water and recycled water can describe different treatment levels and regulatory categories. The connection agreement and laboratory schedule, not the label, should define what the data centre will receive.


2. Confirm the municipal supply and responsibility boundary

A municipal recycled-water connection is an operational relationship as well as a pipe. The project team should establish who owns water quality, pressure, metering, sampling, disinfection residual and incident notification at each boundary. It should also confirm whether the supply is firm, interruptible or subordinate to other users during high demand.


Historical monthly averages are insufficient for a critical cooling application. The utility should provide, where available, time-series quality data, planned and unplanned outage records, minimum and maximum pressure, seasonal capacity and details of changes at the treatment works. The owner should understand how upstream industrial discharges, maintenance, rainfall, network residence time or a change in treatment chemistry could affect the delivered water.


The agreement should define the point of compliance and the procedure for off-spec water. A useful protocol states notification times, sampling methods, decision authority, isolation arrangements and restoration criteria. The data centre then needs enough storage or approved backup supply to respond without losing cooling duty.


Jurisdictional approval remains project-specific. In Abu Dhabi, for example, the Department of Energy has established policy and regulatory requirements for recycled water. Requirements in Dubai and the other emirates may involve different utilities and competent authorities. Early engagement is essential because the permitted use, connection conditions and discharge route can shape the technical concept.


3. Convert historical quality into a design envelope

A design envelope describes the full range of feed conditions the system is required to handle. It should include normal, upper-percentile, maximum and short-duration upset values rather than one favourable analysis. Flow, temperature and pressure belong in the envelope alongside chemistry and microbiology.


Parameters commonly relevant to cooling include conductivity, total dissolved solids and ionic composition; calcium and magnesium hardness; alkalinity and pH; chloride, sulphate and silica; turbidity and suspended solids; iron and manganese; ammonia and phosphate; organic indicators; disinfectant residual; and microbiological activity. The controlling list must be selected for the actual source, metallurgy, treatment process and discharge limit.


Sampling frequency should match variability. Online conductivity and turbidity can reveal rapid changes, while laboratory analysis provides the wider chemical and microbiological picture. Composite samples can describe average loading but may conceal short spikes. Grab samples can capture an event but may not represent normal operation. A suitable programme normally combines both, supported by utility records and event-based sampling.


The envelope should be translated into named design cases: typical operation, summer maximum, high salinity, high suspended solids, elevated organics, low disinfectant residual and supply interruption. Each case should have a defined response. Treatment performance, storage autonomy, cooling-tower cycles and waste flows can then be tested against the same evidence.



4. Establish the water and salt balances

The site water balance should cover utility intake, treatment losses, treated storage, blending, tower evaporation, drift, blowdown, cleaning, overflow, membrane reject and final discharge. Average annual consumption alone cannot size a summer connection, a storage tank or a sewer.


Evaporation is principally set by heat rejection. Increasing cooling-tower cycles reduces blowdown but does not remove the evaporation associated with the thermal load. With negligible drift, blowdown can be approximated as evaporation divided by cycles minus one. At four cycles, an evaporative loss of 100 cubic metres per hour requires roughly 33 cubic metres per hour of blowdown and 133 cubic metres per hour of make-up before other losses.


On-site treatment increases gross intake. If a membrane train supplies that make-up at 80% recovery, feed demand is about 166 cubic metres per hour and approximately 33 cubic metres per hour becomes concentrate. The combined concentrate and tower blowdown may therefore approach 66 cubic metres per hour. Pretreatment backwash and cleaning waste add further hydraulic and chemical loads.


A salt balance is equally important. Evaporation removes water but leaves most dissolved constituents behind. Reverse osmosis transfers much of that salt into a smaller reject stream. The project must demonstrate where the mass of chloride, sulphate, silica, nutrients and treatment chemicals ultimately goes, not only how many cubic metres are reused.


5. Select treatment by controlling constituent

Treatment should close the gap between the feed envelope and the required cooling make-up quality. A robust train may use equalisation, screening, clarification or media filtration, ultrafiltration, hardness control, reverse osmosis, disinfection and final conditioning. Not every project requires every step.


Ultrafiltration provides a strong barrier to suspended solids and can protect downstream membranes, but it does not remove dissolved salts. Reverse osmosis is appropriate when salinity, chloride, sulphate, silica or other dissolved constituents prevent acceptable cooling-tower cycles. Its recovery must be selected against the worst credible feed chemistry and concentrate route, not simply maximised.


Softening can reduce hardness-driven scale and may enable higher tower cycles with less membrane treatment. Activated carbon or another targeted process may be justified when organics, colour or disinfectant by-products affect biological stability or membranes. Final polishing may adjust pH, alkalinity, corrosion tendency or disinfectant residual before storage and blending.


The simplest reliable solution may be partial treatment. A blend of reverse-osmosis permeate and filtered recycled water can meet a defined make-up target while reducing energy and concentrate volume. The blend ratio must be controlled from measured quality and validated against every critical constituent. UF, RO and polishing should be evaluated as parts of one treatment and residuals system.


6. Integrate storage, blending and backup water

Storage provides response time; it does not create supply. Raw recycled-water storage can buffer network pressure changes and short quality excursions. Treated-water storage can cover a treatment trip or provide stable flow to the cooling plant. Backup water protects the site during a longer interruption. Each volume should be derived from a credible scenario and refilling rate.


Tank design must address turnover, temperature, sediment, biological growth, access, cleaning and cross-connection control. Oversized tanks with poor turnover can degrade quality. Undersized tanks can force an immediate transition to backup water during a minor event.


Blending needs a control philosophy. The system should calculate or verify the blend required to meet conductivity, hardness, chloride or other limits, then fail safely if an analyser, valve or source becomes unavailable. Maximum and minimum flow, instrument response time, mixing volume and the location of the compliance sample all affect performance.


The backup transition should be tested. A chemically different potable or desalinated supply can alter corrosion and scale behaviour even when it appears cleaner. Ramp rates, dosing changes and tower-control setpoints should be defined in advance. The detailed approach is covered in Storage, blending and water-quality monitoring.


7. Protect cooling assets and heat-transfer performance

Cooling reliability depends on the recirculating-water condition, not only the make-up specification. As the tower concentrates water, scaling, corrosion and microbiological risks change. The first limiting constituent sets the practical cycles of concentration; conductivity alone cannot identify it.


The treatment programme should reflect the metallurgy, fill, nozzles, heat exchangers, seals and operating temperatures. Calcium carbonate, calcium sulphate, silica, iron deposits and airborne dust can reduce heat transfer or block distribution. Chloride and sulphate can accelerate corrosion. Nutrients and organics can support biofilm, while warm recirculating water and aerosol generation require disciplined public-health controls.


Side-stream filtration may be valuable even when the make-up plant produces low turbidity because GCC dust enters through the tower air path. Deposit inspection, corrosion coupons or probes, microbiological monitoring and periodic heat-transfer assessment provide evidence that the programme is protecting the asset.


Treatment chemicals must be compatible with recycled-water constituents and the approved discharge route. The project should define normal and alarm limits, corrective actions and responsibility between the owner, cooling-equipment supplier and water-treatment provider. See Protecting cooling assets from fouling and corrosion.


8. Monitor the system as one operating process

The utility connection, treatment plant, storage and cooling tower should share one data model. Useful measurements include source and product flow, tank level, pressure, conductivity, pH, turbidity, temperature, disinfectant residual, membrane differential pressure, permeate conductivity, recovery, tower make-up, blowdown and calculated cycles.


Online data provides immediate control; accredited laboratory analysis validates instruments and measures constituents that cannot be monitored continuously. Sampling points should be accessible, representative and labelled. Calibration and maintenance records are part of the evidence, particularly where an analyser initiates diversion or shutdown.


The control system should distinguish a sensor fault from a true water-quality event. Plausibility checks, redundant instruments where justified and time delays can prevent unnecessary trips without allowing sustained off-spec supply. Alarm rationalisation should define priority, response time, operator action and escalation.


Performance reporting should reconcile water and salt balances, treatment recovery, chemical use, off-spec events, backup-water use and tower cycles. Trending these measures reveals slow fouling or utility drift before it becomes a cooling-capacity problem.


9. Resolve blowdown, concentrate and cleaning wastes

Recycled-water use shifts rather than eliminates residuals. Tower blowdown contains concentrated source constituents and cooling chemicals. Reverse-osmosis reject contains much of the dissolved load removed from the make-up. Ultrafiltration backwash, cleaning solutions and tank washdown create intermittent streams with different characteristics.


The project should characterise each stream separately before considering combination. The sewer or other receiver may impose hydraulic, salinity, temperature, pH, biocide, nutrient or suspended-solids limits. A route that accepts normal flow may not accept a simultaneous membrane clean and peak tower blowdown.


Options may include segregation, equalisation, neutralisation, controlled discharge, further recovery or licensed off-site disposal. The correct arrangement depends on local approvals and whole-life cost. Cooling-tower blowdown recovery is valuable only when the remaining concentrate has a reliable destination.


10. Build a defensible commercial case

The comparison should include the recycled-water connection, on-site treatment, tanks, pumps, controls, laboratories, chemicals, power, membranes, cleaning, residual disposal, backup supply, land and operating staff. Avoided potable-water and sewer charges are only part of the case.


Reliability has economic value. A low-cost supply that becomes unavailable during peak wet-bulb conditions may require large backup assets or force derating. Conversely, a well-controlled dual-source arrangement can reduce exposure to water restrictions and support sustainability commitments.


Sensitivity analysis should test source price, connection distance, treatment recovery, worst-case chemistry, disposal cost, power price, membrane life, summer load and phased IT build-out. The preferred concept should remain credible across a reasonable range rather than depend on one optimistic assumption.


Environmental claims should use clear boundaries. Report gross recycled-water intake, net freshwater displacement, consumptive use, discharge, treatment energy and residuals. WUE can support comparison when its boundary and water sources are stated, but it should not replace the full water balance.


11. Use a staged design and commissioning process

Start with a feasibility gate: confirm the heat-rejection demand, utility availability, representative quality data and a plausible residuals route. If any one of these is missing, record the uncertainty before selecting equipment.


Concept design should produce the feed envelope, make-up specification, water and salt balances, treatment philosophy, storage and backup basis, utility interface, control narrative and lifecycle comparison. Piloting is justified when membrane fouling, biological stability, recovery or cleaning frequency cannot be predicted confidently.


Procurement documents should state the full feed envelope, product limits, duty, turndown, recovery, availability, consumptions, waste characteristics and acceptance tests. Factory and site testing should prove automatic diversion, standby capacity, backup transition, analyser failure response and recovery after an upset.


Commissioning should use representative water, calibrated instruments and agreed success criteria. A reliability run, operator training, spares, maintenance plans and a complete data handover are required before sustained operation. The result should be an operating water system, not merely an installed treatment skid.


12. How Crescent Engineering can support the project

Crescent Engineering can develop the source assessment, treatment design basis, water and salt balances, packaged treatment scope, storage and blending philosophy, controls, commissioning plan and lifecycle support model. The work can begin with a feasibility memorandum, sampling plan or pilot brief and progress into detailed equipment and service delivery.


To start, provide the proposed cooling schematic, heat-rejection duty, utility quality records, available flow and pressure, intended backup source, discharge information and project phasing.



13. References and further reading

Final water-quality limits, public-health controls, utility conditions and discharge requirements must be confirmed for the specific site and jurisdiction.


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