Data Center Process Water Tank: Cooling Makeup, RO Reject And Chemicals
Created on 10.30
Data Center Process Water Tank: Cooling Makeup, RO Reject And Chemicals
A data center process water tank is the non-chilled reserve that feeds the cooling plant's supporting water needs: cooling-tower makeup, reverse-osmosis (RO) reject containment, and chemical-dosing day tanks for scale and corrosion control. It is distinct from a chilled-water thermal energy storage tank, which holds conditioned water for cooling load shifting; the process tank holds utility and chemical streams at ambient condition. Material selection follows the chemistry of each stream — makeup is low-mineral or reclaimed, RO reject is concentrated and scaling-prone, and chemical day tanks hold aggressive dosing concentrates — and the fabrication is referenced to AWWA D103-09 with NSF/ANSI 61 and WRAS-listed linings where water contact occurs.
The water side of a data-center cooling plant is broader than the chilled-water loop most people picture. Behind every cooling tower sits a set of supporting streams — makeup to replace evaporative loss, RO reject from any on-site water polishing, and the chemical concentrates that keep the tower from scaling and corroding. Each needs containment, and lumping them into one undefined "water tank" leads to cross-contamination, scaling, or a lining destroyed by dosing chemical. The discipline is to separate the streams and specify each container to its actual chemistry, keeping the process tank clearly distinct from the chilled-water TES vessel.
This guide sets out how a data center process water tank serves cooling makeup, RO reject and chemical duty, and how to specify each correctly.
Cooling Makeup: The Largest Process Draw
Cooling-tower makeup is the dominant process-water demand on a data-center campus, and the makeup tank is the buffer between supply and evaporative loss. Evaporation, drift and blowdown constantly remove water that makeup must replace.
1. Makeup sources. Potable, reclaimed or recovered condensate, blended to keep tower conductivity within limits.
2. Buffer role. The makeup tank holds enough reserve to cover supply interruption and peak evaporation without the tower tripping on low level.
3. Water-contact lining. Because makeup ultimately enters a system that can create aerosols, the lining is specified to NSF/ANSI 61 and WRAS for non-potable water contact.
The makeup tank is sized to the evaporation and blowdown balance, not to the chilled-water or fire systems, and it is the first process stream a campus should engineer for water efficiency.
RO Reject: Containing The Concentrate
Reverse-osmosis reject is the concentrated side stream of any on-site desalination or polishing skid, and it is far more scaling-prone than the feed it came from. It must be contained, not poured into a generic tank.
· Concentrated dissolved solids. RO reject carries everything the permeate left behind, so its scaling and corrosion potential is higher than the source water.
· Containment, not blending by default. It is held for managed discharge, further concentration, or controlled reuse (such as tower makeup at a bounded rate) rather than dumped into the makeup reserve unchecked.
· Lining tolerance. The container lining must tolerate the elevated TDS and any antiscalant or pH-adjustment chemistry, favouring GFS enamel or a documented FBE grade.
Used carefully, RO reject can offset some makeup demand, but only with conductivity monitoring and a lining rated for the concentrate.
Stream | Chemistry | Container requirement |
Cooling makeup | Low to moderate TDS | NSF/ANSI 61, WRAS lining |
RO reject | High TDS, scaling-prone | Enamel or rated FBE, monitoring |
Chemical day tank | Aggressive concentrate | Chemical-resistant, dedicated |
Chemical Dosing Day Tanks
Chemical day tanks hold the concentrated scale and corrosion inhibitors, biocides and pH adjusters that keep the cooling loop alive, and they are a separate, dedicated class of vessel. These are not water tanks in the storage sense; they are small, chemical-resistant containers feeding metered dosing pumps.
· Scale and corrosion inhibitors. Phosphonates, molybdates or similar, dosed to keep the tower-side chemistry controlled.
· Biocides. Oxidising or non-oxidising agents to limit microbial growth and legionella risk in the tower basin.
· Acid or alkali for pH. Used where the makeup or reject chemistry pushes the loop out of its safe pH band.
· Dedicated, labelled, bunded. Each day tank is isolated, labelled and, where spill risk demands, bunded so a leak cannot reach the process or fire systems.
Keeping chemical day tanks separate from the bulk process reserve prevents a dosing accident from contaminating the entire makeup volume.
Material And Coating By Stream
Each process stream gets the lining its chemistry requires, and the tank material is chosen so the shell is never the weak point. Bolted steel with a certified lining covers most duties.
· GFS (glass-fused-to-steel). Enamel fired at 820–930 °C gives a smooth, chemically resistant skin (Ra < 0.8 µm, adhesion above 3,450 N/cm²) suited to makeup, reject and many chemical-adjacent duties; every panel is spark-tested at 1,500 V DC.
· FBE (fusion-bonded epoxy). A documented lining (AWWA C550-style) chosen where a specified coating grade and pH tolerance are required.
· Stainless. Selected for chemical day tanks or clean streams where a factory vessel with passivated internals is preferred.
· Galvanized (limited). Milder, non-contact process duty only.
NSF/ANSI 61 and WRAS listings apply to any lining contacting water destined for the cooling system; chemical day tanks carry chemical-resistance certification instead.
Duty | Recommended material | Lining / certification |
Makeup reserve | GFS or FBE bolted | NSF/ANSI 61, WRAS |
RO reject | GFS or rated FBE bolted | Enamel or rated epoxy |
Chemical day tank | Stainless or lined vessel | Chemical-resistant, bunded |
Mixed clean process | GFS bolted | ISO 28765, spark test |
Distinct From Chilled-Water TES
The process water tank must not be confused with the chilled-water thermal energy storage tank, which performs a different function at a different temperature. This distinction prevents mis-specification.
· Process tank. Ambient-condition utility and chemical containment — makeup, reject, dosing — feeding and protecting the cooling plant.
· Chilled-water TES. A stratified or ice/thermal store holding conditioned water (or ice/PCM) for load shifting and peak shaving of the cooling load, engineered to thermal, not just containment, performance.
· Why it matters. Sizing, insulation, lining and controls differ; specifying a process tank where a TES is needed (or vice versa) produces a system that cannot do its job.
The two are complementary on a campus but are engineered as separate, clearly-bounded assets.
Project Case
A dedicated data-center process-water reference is not yet part of the delivered portfolio, so this article is written as engineering guidance rather than a project citation. The company's capability to supply bolted water and process tanks across materials is demonstrated in adjacent sectors: overseas fire-protection programs have delivered GFS tanks up to 12,261 m³ (India, 3 tanks, 2024-06) and 1,666 m³ (Singapore, 2 tanks, 2026-01), built to the same bolted-tank standards a data-center process water tank is engineered to. Those references evidence large-volume bolted-tank supply and QA; they are fire-protection projects, not data-center process-water installations, and are cited here only as capability context.
Center Enamel Engineering Capability
Center Enamel (Shijiazhuang Zhengzhong Technology Co., Ltd) has designed and fabricated bolted storage tanks since 2008. As the first glass-fused-to-steel (GFS) tank manufacturer in China, the company holds close to 200 enamel-related patents, produces roughly 300,000 enamel-coated steel plates a year, has completed more than 30,000 installed projects and supplies its tanks to over 100 countries. The new 150,000 m² production base was added to raise output capacity, and single tanks are supplied up to 60,000 m³. Manufacturing runs under ISO 9001 and ISO 45001, with product certification including NSF/ANSI 61, WRAS, FDA, LFGB, CE (EN 1090), ISO 28765, FM, BSCI and EUROCODE, and design referenced to AWWA D103-09, AWWA C550, ISO 28765, NSF/ANSI 61 and WRAS where the application requires it.
For data-center process-water duty the company supplies GFS, FBE, stainless and galvanized bolted tanks with linings specified per stream — NSF/ANSI 61 and WRAS for water-contact makeup, enamel or rated FBE for RO reject, and dedicated chemical-resistant day tanks — with coating and spark-test documentation for review.
Frequently Asked Questions
Q1: What is the difference between a process water tank and a chilled-water TES tank?
A1: A process tank holds ambient utility and chemical streams (makeup, RO reject, dosing) for the cooling plant; a chilled-water TES tank stores conditioned water or ice/PCM for cooling load shifting. They are separate, differently engineered assets.
Q2: How is cooling makeup volume set?
A2: By the evaporation, drift and blowdown balance of the cooling towers, sized so the makeup reserve covers supply interruption and peak loss without tripping the tower on low level.
Q3: Can RO reject go into the makeup tank?
A3: Only with conductivity monitoring and a lining rated for the concentrate; RO reject is scaling-prone and should be contained or bounded-rate blended, not dumped unchecked.
Q4: Why are chemical day tanks separate?
A4: They hold aggressive dosing concentrates; a dedicated, labelled, bunded vessel prevents a leak or dosing error from contaminating the entire makeup reserve.
Q5: Which lining suits process duty?
A5: GFS enamel for makeup, reject and many adjacent duties (Ra < 0.8 µm, 1,500 V DC spark test); documented FBE where a coating grade is specified; stainless for chemical day tanks or clean streams.
Q6: What certification applies to makeup contact?
A6: NSF/ANSI 61 and WRAS listings confirm the lining is acceptable for contact with water intended for non-potable cooling use; chemical day tanks carry chemical-resistance certification instead.
Q7: How is the process tank material chosen?
A7: By each stream's chemistry — pH, TDS, scaling and chemical aggression — matched to a lining that can be documented to the relevant standard such as AWWA D103-09 or ISO 28765.
A data center process water tank serves the cooling plant's supporting water needs — makeup, RO reject containment and chemical day tanks — and must be kept distinct from the chilled-water TES vessel that shifts cooling load. Separate the streams, specify each lining to its chemistry with NSF/ANSI 61 and WRAS for water contact, contain RO reject and chemical concentrates in dedicated vessels, and reference the fabrication to AWWA D103-09 and ISO 28765. Done that way, the process side of the plant is contained, controllable and efficient rather than a single undefined liability.
Talk to an Engineer
For a data center process water tank, send us your cooling-tower makeup balance, any RO reject stream and its TDS, the chemical dosing concentrates you use, and the fabrication standard required. We will return a per-stream material and lining recommendation with NSF/ANSI 61 / WRAS or chemical-resistance certification, a sizing study for the makeup and reject reserves, and a specification for GFS, FBE, stainless or galvanized bolted tanks with coating and spark-test documentation.
WhatsApp