GRP Cold Water Tanks in High-Rise and Multi-Storey Buildings
The complete specification, compliance, and maintenance reference for consulting engineers, MEP contractors, and facilities managers involved in cold water storage in UK multi-storey developments.
Key facts at a glance
1K–4.6M
Sectional water tank components
25–30
Year design life with correct installation and maintenance
<20°C
Cold water storage target under HSG274 Part 2 and ACoP L8
Cat. 5
Fluid category — requires Type AG or AA air gap at inlet
1,000 L
Threshold above which statutory notification is required
750 mm
Minimum doorway width through which sectional panels can pass
01
Definition & context
What is a sectional GRP cold water tank?
A sectional GRP cold water tank is a modular water storage vessel assembled on-site from glass reinforced plastic panels bolted to a structural frame, with joints sealed and internal bracing installed as required. Individual panels pass through standard doorways of 750 mm or wider.
GRP does not corrode in the way that ferrous metals do, has a high strength-to-weight ratio, and is available in formulations approved for contact with drinking water.
Product standard: Product standard: BS EN 13280. Products in potable water contact must be certified under Regulation 4(1)(a) of the Water Supply (Water Fittings) Regulations 1999. Accepted schemes include WRAS (wras.co.uk) and Kiwa KUKreg4 (kiwa.com/uk). Verify current certification status at procurement; certifications can lapse.
Sectional vs one-piece GRP
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Factor
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Sectional
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One-Piece
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|---|---|---|
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Capacity
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No upper limit
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Up to ~16,000 L
|
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Site access
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750 mm doorway
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Full unit entry
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|
Configuration
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Any combination
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Fixed as moulded
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Restricted rooms
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Only if tank fits
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Primary advantage
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02
System design
Why high-rise buildings use sectional GRP tanks
Pressure management
Supplying upper floors directly from mains is often impractical. Break-tank-and-booster arrangements are required above approximately five or six storeys.
Peak demand buffering
Stored volume absorbs demand peaks and reduces the required size of the incoming main connection.
Access and space
Sectional construction is the only practical way to install large-volume tanks in plant rooms accessed through standard doorways or stairwells.
CIBSE Guide G notes that low-level break tanks and booster sets can reduce contamination risk compared with rooftop cisterns.
Typical system configurations
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Configuration
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Typical application
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|---|---|
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Capacity
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No upper limit
|
|
Site access
|
750 mm doorway
|
|
Configuration
|
Any combination
|
|
Restricted rooms
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Only if tank fits
|
03
Standards & specification
Specification, standards, and design life
BS EN 13280 — product standard
The European standard specifying requirements for GRP cisterns and sectional tanks for above-ground cold water storage, covering material composition, structural performance, dimensional tolerances, water tightness, and hygiene suitability.
Regulation 4(1)(a) — Water Supply (Water Fittings) Regulations 1999
Regulation 4(1)(a) of the Water Supply (Water Fittings) Regulations 1999 requires that water fittings meet an appropriate quality and standard to prevent contamination, waste, or misuse of the public water supply. Tricel’s sectional GRP tanks carry this certification — commonly referenced as KUKreg4 — confirming that the tanks’ non-metallic materials have been tested to BS 6920 for suitability with potable water, and that appropriate measures are in place to manage Fluid Category 4 risks, which cover fluids presenting a significant health hazard. Current approval status can be verified at wras.co.uk.
Design life: 25–30 years with correct installation and maintenance. Inadequate base levelling is the most common cause of premature joint failure
Capacity ranges
|
Capacity
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Typical Applications
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|---|---|
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1,000–5,000 L
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Smaller multi-residential, light commercial break tanks
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5,000–30,000 L
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Mid-size commercial, mixed-use multi-storey
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30,000–100,000 L
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Large commercial, hotel, hospital, high-rise residential
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100,000 L+
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Campus, hospital complex — bespoke design required
|
04
Design Methodology
Sizing cold water storage for high-rise buildings
Four competing design requirements
- Peak demand buffering — what draw-off rate must storage sustain, and for how long?
- Resilience — how many minutes of service under loss of mains supply?
- Water hygiene — what maximum residence time is acceptable given Legionella risk profile?
- Physical constraints — footprint, height, and structural floor loading available
Two-compartment arrangements are strongly recommended for residential buildings above five storeys and any building where supply interruption creates significant welfare or commercial impact.
Thermal stratification — risks and controls
In tanks above approximately 10,000 L, warmer less dense water rises to upper layers while cooler water settles below. Upper layers may exceed 20°C and enter the Legionella risk range even when a single sensor reading appears acceptable.
- Multiple temperature sensors at low, mid, and high levels
- Diagonal inlet/outlet positioning to promote end-to-end turnover
- Internal baffles to force a defined flow path from inlet to outlet
05
Regulatory compliance
UK compliance for cold water storage tanks
Water fittings regulation is a devolved matter in the UK. There are three separate legal instruments — always reference the correct instrument for your jurisdiction.
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Jurisdiction
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Primary legislation
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Enforced by
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|---|---|---|
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England & Wales
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Water Supply (Water Fittings) Regulations 1999 (SI 1999/1148)
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Water undertakers
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Scotland
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Water Supply (Water Fittings) (Scotland) Byelaws 2014
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Scottish Water
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Northern Ireland
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Water Supply (Water Fittings) Regulations (NI) 2009, SR 2009/255
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NI Water
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Statutory notification
Regulation 5 requires notification to the water undertaker before installing any storage vessel exceeding 1,000 litres. Failure to notify is a criminal offence. Notification must be submitted before work commences.
Do not assume England and Wales legislation applies UK-wide. Citing only SI 1999/1148 is incorrect for Scottish or Northern Irish projects.
Fluid category 5 & backflow prevention
A cold water storage cistern is classified as Fluid Category 5. The only compliant backflow prevention at the cistern inlet is an air gap device — Type AA or Type AG. The minimum free air gap is 20 mm or twice the internal diameter of the inlet pipe, whichever is greater.
RPZ valves and non-return valves cannot be used to protect against Category 5 backflow risk.
06
Water hygiene
Sizing cold water storage for high-rise buildings
Temperature thresholds (HSG274 Part 2 / ACoP L8)
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Temperature
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Significance
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|---|---|
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<20°C
|
Target storage and distribution temperature
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20–45°C
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Range in which Legionella can survive and multiply
|
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~37°C
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Optimal growth temperature for Legionella pneumophila
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>20°C in storage
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Control failure — triggers investigation under written scheme
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Dutyholder obligations — ACoP L8
- Identify and assess sources of Legionella risk — written risk assessment
- Prepare a written scheme of precautions describing control measures
- Implement, manage, and monitor precautions
- Keep records of all monitoring, inspection, and cleaning
- Appoint a responsible person to manage compliance
- Annual cleaning and disinfection is the minimum baseline per HSE guidance. The precise frequency is set by the site Legionella risk assessment.
07
Installation
Installation: practical guidance
Pre-installation checklist
- Access route survey — measure all doorways, stairwells, corridors
- Base readiness — level tolerance ±3 mm, structural load confirmed
- Drainage — floor drain capacity and overflow discharge route
- Thermal environment — plant room temperature profiled
- Isolation strategy — valves and bypass confirmed before work
Base levelling
Inadequate base levelling is the most common cause of premature joint failure. Check level in two axes across the full footprint — not only at corners
Re-torque is not optional. GRP seals compress after first fill and thermal cycling. Skipping this step is the most common cause of early joint leaks.
Assembly and first-fill requirements
- Complete structural frame before introducing panels
- Apply specified torque values — calibrated torque wrench, record all values
- Install tie rods and internal bracing exactly as specified
- Fill to operational level then re-torque all bolts — not optional
- Post-settlement re-torque at 4–6 weeks after initial fill
08
Operation & maintenance
Operation and maintenance
Under the Water Supply (Water Fittings) Regulations and HSE’s ACoP L8, the building owner or person responsible for the premises is legally accountable for the water system throughout its operating life.
Maintenance frequency schedule
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Frequency
|
Key Tasks
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By
|
|---|---|---|
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Weekly
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External leak check, lid integrity, plant room temp
|
FM team
|
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Monthly
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Float valve, inlet screens, insulation condition
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FM / contractor
|
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Quarterly
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Internal visual, sediment, BMS alarm test
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Specialist contractor
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Six-Monthly
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Temperature monitoring, microbiological sampling
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Hygiene contractor
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Annually
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Full internal inspection, clean & disinfect, bolt re-torque
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Specialist contractor
|
Confined space entry
Entry into a drained cold water tank is a confined space entry under the Confined Spaces Regulations 1997. All entries require a written safe system of work, atmospheric testing, a trained standby person outside, and emergency rescue equipment.
Only trained and authorised personnel may enter a confined space. Verify contractor competence and confined space training records before commissioning any cleaning work.
Case study — City of London, EC3
20 Fenchurch Street (The ‘Walkie Talkie’)
38-storey, 160-metre office tower. Four sectional GRP hot-press tanks installed across plant levels with coordinated lifting, levelling steelwork, and interconnecting pipework under a single-point responsibility arrangement
302,000
Litres total installed capacity across 4 sectional GRP tanks
Frequently asked questions
What is a sectional GRP cold water tank?
A sectional GRP cold water tank is a modular water storage vessel assembled on-site from glass reinforced plastic panels bolted to a structural frame and sealed at joints. The sectional construction allows panels to be passed through standard doorways and assembled in restricted plant rooms, making it the dominant choice for large-volume cold water storage in high-rise and multi-storey buildings. See Section 2 for a full definition.
What is the difference between a GRP tank and a GRP cistern?
The terms are used interchangeably in practice. Technically, a cistern is open to atmosphere (vented), while a tank may be pressurised or sealed. Most cold water storage vessels in high-rise and multi-storey buildings are vented cisterns. The Water Fittings Regulations refer to storage cisterns; industry practice uses tank. Both refer to the same product in this context.
How long does a sectional GRP cold water tank last?
A correctly installed and maintained sectional GRP tank can achieve a design life of 25–30 years or more. The principal factors affecting longevity
are base levelness, maintenance of joint seals (periodic bolt re-torque), quality of the panel resin system, and whether the tank is protected from UV (for external installations). Neglected maintenance significantly shortens service life.
Does a GRP cold water tank require Regulation 4(1)(a) certification?
Regulation 4(1)(a) of the Water Supply (Water Fittings) Regulations 1999 requires that fittings in contact with potable water do not contaminate the water supply and are mechanically fit for purpose. Independent certification is not a statutory obligation in every instance, but it is the accepted means
of demonstrating compliance and is required by most water companies and project specifications. Two schemes currently operate in the UK: WRAS and Kiwa KUKreg4. Always verify current certification status at wras.co.uk or kiwa.com/uk; certifications can lapse.
What fluid category is a cold water storage cistern?
The water in a cold water storage cistern is classified as Fluid Category 5 under the Water Fittings Regulations — a fluid presenting a serious health
hazard. This means the inlet to the cistern from he mains supply must be protected by an air gap device (Type AA or Type AG air gap). Mechanical backflow prevention devices such as non-return valves or RPZ valves cannot protect against Category 5 risk. See Section 7.3.
What type of air gap is required at a cistern inlet?
The standard backflow prevention arrangement for a cold water storage cistern inlet is a Type AG air gap — a float valve whose outlet terminates above the cistern overflow spillover level. The minimum free air gap is 20mm or twice the internal diameter of the inlet pipe, whichever is greater. This must be maintained under all operating conditions including maximum fill rate.
How should the overflow pipe on a cold water tank be sized?
Size the overflow pipe for at least 1.5 times the maximum inlet flow rate under fault conditions — that is, when the float valve is fully open at maximum available mains pressure. This safety factor allows for partial blockage over time. Select pipe bore using standard flow calculations for the available head and discharge route. The overflow must discharge to a visible, traceable point; do not route to a concealed drain. See Section .4 for the full methodology.
What temperature should a cold water storage tank be kept at?
HSE guidance (HSG274 Part 2 and ACoP L8) specifies that cold water should be stored and distributed at or below 20°C. Legionella bacteria can survive and multiply at temperatures between 20°C and 45°C, with optimal growth at approximately 37°C. Cold water tanks in warm plant rooms must be insulated and monitored to confirm that stored water remains below the 20°C threshold.
How often should a cold water tank be cleaned?
Annual cleaning and disinfection is the minimum baseline per HSE guidance and the standards referenced by the DWI (BS EN 806-5 and BS 8558). The exact frequency should be determined by the site Legionella risk assessment. Tanks in high-risk environments — warm plant rooms, buildings with immunocompromised occupants, or following positive Legionella sampling — may require more frequent cleaning.
What regulations apply to cold water tanks in Scotland?
In Scotland, the applicable legislation is the Water Supply (Water Fittings) (Scotland) Byelaws 2014, made by Scottish Water under the Water (Scotland) Act 1980, s.70. These Byelaws are not a statutory instrument and carry no SSI number. They are enforced by Scottish Water. The requirements are substantively the same as the 1999 Regulations in England and Wales — including backflow prevention, overflow arrangements, and material suitability — but the Scottish instrument must be cited in Scottish project documentation. Building services standards (BS EN 13280, BS EN 806-5, HSE ACoP L8) apply UK-wide.
What regulations apply to cold water tanks in Northern Ireland?
In Northern Ireland, the applicable legislation is the Water Supply (Water Fittings) Regulations (Northern Ireland) 2009 (SR 2009/255), enforced by
Northern Ireland Water. Requirements are substantively the same as the 1999 Regulations in England and Wales. Always reference the correct instrument in Northern Ireland project documentation.
What is Building Regulations Part G and does it apply to cold water tanks?
Part G of the Building Regulations 2010 (England and Wales) covers Sanitation, Hot Water Safety and Water Efficiency. Requirement G1 requires that premises are provided with a sufficient supply of wholesome water. Cold water storage tanks supplying domestic cold water services in new or altered buildings must be designed and installed to comply with G1, including protection from contamination and adequate capacity. Approved Document G references the Water Supply (Water Fittings) Regulations as the accepted compliance route.
What are the options for water treatment in a cold water tank?
Where physical controls alone are insufficient to manage Legionella risk — for example in buildings where stored cold water temperature cannot reliably be kept below 20°C — three supplementary treatment options are available: UV disinfection (point-of-treatment inactivation; no residual protection); chlorine dioxide dosing (residual biocide; requires careful control within drinking water limits); and copper-silver ionisation (residual protection; requires ion concentration monitoring). Selection should be part of the Legionella risk assessment. See Section 8 for full details.
What is thermal stratification and why does it matter in large cold water tanks?
Thermal stratification occurs when warmer, less dense water rises to the upper layers of a large storage tank while cooler water settles lower. In a multi-storey plant room with heat gain, the upper layers of a large tank can exceed 20°C — entering the Legionella risk range — even when average temperature or a single low-level sensor reading appears acceptable. Mitigation measures include multiple temperature sensors at different heights, internal baffles to promote mixing, and correct inlet/outlet positioning.
Can I install a sectional GRP tank in a confined plant room?
Yes — this is the primary design advantage of sectional GRP construction. Panels can be carried through standard doorways (typically 750 mm minimum) and assembled in-situ. Complete an access route survey before delivery to confirm panel dimensions are compatible with available openings, turns, stairwells, and lift capacity. Prepare a handling method statement and lifting plan before delivery.
Does a cold water storage tank need to be notified to the water company?
Yes. Regulation 5 of the Water Supply (Water Fittings) Regulations 1999 — and equivalent provisions in Scotland and Northern Ireland — requires
notification to the relevant water undertaker before installing any water storage vessel with a capacity exceeding 1,000 litres. Most multi-storey
installations exceed this threshold. Failure to notify is a criminal offence. Notification must be submitted before work commences; the undertaker has
ten working days to respond.
What is the Building Safety Act 2022 and does it apply to cold water tanks?
The Building Safety Act 2022 (BSA) introduces a separate dutyholder regime for occupied higher-risk buildings in England — defined as buildings of at least 18 metres or seven storeys containing at least two residential units. The Principal Accountable Person (PAP) under the BSA holds obligations that sit alongside, and do not replace, the ACoP L8 Legionella control duties. The written Legionella control scheme and the Building Safety Case should be treated as complementary documents. The BSA applies in England; Scotland, Wales, and Northern Ireland have separate devolved frameworks.
Can a sectional GRP cold water tank be installed on a roof?
Yes, but rooftop installations carry specific risks that require careful design attention: UV exposure requires UV-stabilised panel grades; thermal extremes (summer heat and winter frost) demand significantly greater insulation; structural loading at roof level must be assessed by a structural
engineer; and safe working at height must be provided for ongoing maintenance access. Rooftop gravity storage is less favoured in modern practice than low-level break-tank-and-booster arrangements. See Section 4.4 for a full comparison of installation locations.
RELATED TECHNICAL GUIDES
GO DEEPER ON THE TOPICS THAT MATTER
Each article in this series covers a specific aspect of cold water storage in multi-storey buildings at full technical depth, with compliance references, worked examples, and checklists.
Technical Guide
Cold Water Tank Sizing for Multi-Storey Buildings
Demand calculations, CIBSE methodology, worked examples, and two-compartment sizing rationale.
Technical Guide
Break Tanks and Booster Sets: Design Guide
Hydraulic design, pressure zoning, pump selection, and booster set interface with cold water storage.
Standards & Compliance
Legionella Risk Assessment for Building Water Systems
Written risk assessment methodology, risk factor identification, and written control scheme.
Technical Guide
Cold Water Commissioning:
BS EN 806-5
Step-by-step commissioning procedure, chlorination methodology, and handover documentation.
Standards & Compliance
Backflow Prevention: Fluid Categories and Device Selection
Fluid category classification, air gap types, and correct backflow prevention device specification.
Standards & Compliance
Confined Space Entry in Building Maintenance
Legal obligations under the Confined Spaces Regulations 1997 and safe systems for tank cleaning.
White paper — April 2026 · 70 pages
Sectional GRP Cold Water Tanks in High-Rise Buildings
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We supply and install sectional GRP cold water tanks across the UK — capacity from 1,000
litres to 4.6 million litres in high-rise commercial, residential, healthcare, and industrial buildings.
This guide is provided for general guidance and information purposes only. It does not constitute engineering advice and should not be relied upon as the sole basis for design decisions. © 2026 Tricel Water. All rights reserved.
