GRP Category 5 Break Tanks
Tricel manufactures GRP Category 5 break tanks with a factory-fitted Type AB air gap — the highest level of backflow protection for mains water connections. WRAS approved and compliant with the Water Supply (Water Fittings) Regulations 1999. Required wherever a mains connection supplies a system presenting a fluid category 5 contamination risk.
- •Fluid category 5 — highest risk classification under the Water Fittings Regulations
- •Type AB air gap: raised float valve housing with weir overflow — factory fitted
- •WRAS approved — compliant with the Water Supply (Water Fittings) Regulations 1999
- •Non-mechanical device: permanent physical air gap — no valves, no failure modes
- •Insulated and uninsulated options; UK manufacturer – Tricel Water UK
Cat 5 Break Tank - Specification
Air gap type
Type AB (raised housing + weir)
Fluid category
Category 5 - highest risk
Regulation
WSFR 1999 / Scottish Byelaws 2004
Approval
WRAS approved
Construction
Single moulded GRP unit
Insulation
Insulated & uninsulated options
Manufacturer
Tricel Water UK - UK manufacturer
What is a Category 5 break tank?
A Category 5 break tank is a cold water storage tank fitted with a Type AB air gap — a raised float valve housing with a weir overflow — that provides the highest level of backflow protection against fluid category 5 contamination risks under the Water Supply (Water Fittings) Regulations 1999. Fluid category 5 describes fluids presenting a serious health hazard due to the presence of pathogenic organisms, highly toxic or radioactive substances, or faecal, human or animal waste. The AB air gap is a non-mechanical device: the mains inlet is positioned in a raised housing above the tank lid, and the weir overflow is located below the inlet but above the maximum water level inside the tank. If the float valve fails and water rises, the excess spills through the weir before reaching the inlet pipe — making contamination of the public supply physically impossible even under vacuum conditions. Tricel Water UK manufactures WRAS-approved GRP Category 5 break tanks in insulated and uninsulated configurations as part of its GRP one-piece tank range.
01
Fluid Categories
Understanding Fluid Categories and Why Category 5 Requires a Break Tank
The Water Supply (Water Fittings) Regulations 1999 classify fluid contamination risks into five categories. Each category determines the level of backflow protection required on the mains connection. Category 5 — the highest — demands a Type AB air gap. A standard AG air gap tank is not sufficient.
|
Category
|
Risk level
|
Fluid description
|
Typical examples
|
Min. backflow protection
|
|---|---|---|---|---|
|
1
|
No risk
|
Wholesome water from the public supply
|
Mains drinking water as supplied
|
None required
|
|
2
|
Very low
|
Slight aesthetic change — taste, odour or colour from approved substances
|
Water coolers, water softeners, domestic water heaters
|
Type AG air gap or check valve
|
|
3
|
Slight hazard
|
Slight health hazard — substances permitted in food preparation
|
Domestic washing machines, garden taps, irrigation of food crops
|
Type AG air gap or RPZ valve
|
|
4
|
Significant hazard
|
Significant health hazard — toxic substances not permitted in food prep
|
Cooling towers, car wash pre-soak, swimming pool chemicals, commercial irrigation
|
Type AG air gap or approved RPZ valve
|
|
5
|
Serious hazard
|
Serious health hazard — pathogenic organisms, highly toxic or radioactive substances, faecal or human/animal waste
|
Laboratories, mortuaries, veterinary practices, hospitals (clinical), agricultural livestock systems, bin stores
|
Type AB air gap only
|
The fluid category is determined by the risk of the downstream system – not the water stored in the tank. A mains connection serving a laboratory handwash basin presents a category 5 risk even if the tap water itself is wholesome. The responsible person, water undertaker or a competent water regulations inspector must confirm the required category for each installation. Do not self-determine fluid category.
02
The AB Air Gap
The Type AB Air Gap - Why It Provides Category 5 Protection
A Type AB air gap is the only non-mechanical backflow prevention device accepted for fluid category 5 protection under the Water Supply (Water Fittings) Regulations 1999. Its protection is absolute because it contains no valves, seals or moving parts that can fail.
Raised inlet housing — The mains water inlet is positioned in a housing mounted above the tank lid. There is a permanent physical gap between the inlet and any water inside the tank.
Weir overflow — A weir overflow is positioned below the inlet pipe but above the maximum water level inside the tank. If the float valve fails and water rises, it spills through the weir before it can reach the inlet.
No mechanical components — Unlike RPZ valves or check valves, the AB air gap has no parts to fail, scale, stick or degrade. Protection is maintained continuously without maintenance of the backflow device itself.
Vacuum-proof — Even if a pressure drop creates a negative vacuum on the mains supply, water inside the tank cannot be siphoned back through the inlet pipe because there is no physical connection between the tank water and the inlet.
Factory fitted by Tricel — The raised housing and weir are fitted during manufacture and form part of the WRAS-approved tank assembly. The AB air gap is not retrofitted — it is integral to the tank specification.
The WRAS approval covers the complete tank assembly including the AB air gap arrangement. Modifying the raised housing, changing the weir position or adding non-approved fittings may invalidate the WRAS approval. Confirm any modifications with Tricel before the tank is installed.
03
Applications
Where Category 5 Break Tanks Are Required
Category 5 backflow protection is required wherever a mains water connection serves a system presenting a fluid category 5 contamination risk. The following building types and applications commonly require Cat 5 protection — but this list is indicative only.
Healthcare & NHS
Hospitality & Leisure
Infrastructure & Utilities
Fire Protection
High-Rise & Multi-Storey
Industrial & Manufacturing
Education
Agriculture
Food & Beverage
Local Authority & Public
The required fluid category for any specific installation must be confirmed by the water undertaker or a competent person registered under an Approved Contractor Scheme. Do not determine fluid category without a formal assessment.
This list is indicative only. The presence of a Cat 5 risk depends on the specific activities, substances and water uses at each installation. The water undertaker or a competent person must assess and confirm the required fluid category. Regulation 5 requires prior notification to the water undertaker before certain high-risk installations proceed.
04
Product Specification
Tricel GRP Category 5 Break Tank — Product Specification
Tricel’s Category 5 break tanks are manufactured as part of the GRP one-piece tank range. The AB air gap arrangement — raised housing and weir overflow — is factory fitted during manufacture and forms part of the WRAS-approved tank assembly.
|
Parameter
|
Specification
|
|---|---|
|
Tank construction
|
Single moulded GRP unit — no joints or internal seams
|
|
Air gap type
|
Type AB — raised float valve housing with weir overflow
|
|
Fluid category protection
|
Category 5 (highest level)
|
|
Regulation
|
Water Supply (Water Fittings) Regulations 1999; Scottish Water Byelaws 2004
|
|
Approval
|
WRAS approved (tank assembly including AB air gap)
|
|
GRP standard
|
BS EN 13280:2001 — GRP cold water storage
|
|
BS EN 1717
|
European standard for backflow prevention in drinking water installations
|
|
Insulation
|
CFC-free PU foam (insulated option) / uninsulated option available
|
|
Insulated max temp
|
23°C (WRAS potable) / 30°C (general storage)
|
|
Screened vent / overflow
|
Factory fitted — prevents ingress of insects and debris
|
|
Float valve sizing
|
Confirmed to incoming mains supply diameter at order
|
|
Manufacturer
|
Tricel Water UK — UK manufacturer
|
Tricel provides WRAS approval documentation on request. WRAS documentation is available for inclusion in project O&M manuals, procurement submissions and water undertaker notifications.
Air gap
Type AB
Raised housing + weir
Protection
Cat 5
Highest risk level
Approval
WRAS
Full assembly
Mechanism
None
Non-mechanical device
Factory-fitted AB air gap — why this matters
Integral to the WRAS-approved assembly
The AB air gap housing is factory fitted by Tricel during manufacture and forms an integral part of the WRAS-approved tank. It is not retrofitted on site. This means the approval covers the complete assembly — tank body, raised housing, weir overflow and screened vent — as a single certified unit, reducing the risk of field installation error invalidating the backflow protection.
05
AG vs AB Air Gap
AG Air Gap vs AB Air Gap: What Is the Difference?
The standard Tricel one-piece GRP tank is supplied with an AG (Type AG) air gap — suitable for fluid categories 1 to 4. Where a fluid category 5 risk is present, the AB (Type AB) air gap tank is required instead. The two products look similar but serve different regulatory purposes.
Fluid Categories 1–4
Standard One-Piece Tank — AG Air Gap
- Float valve fitted within the body of the tank at standard lid level
- AG air gap is the vertical distance between the inlet and the water surface
- Provides backflow protection from fluid categories 1 to 4
- Suitable for the majority of commercial and residential applications
- Not suitable for fluid category 5
Fluid Category 5
Category 5 Break Tank — AB Air Gap
- Float valve and inlet mounted in raised housing above the tank lid
- Weir overflow positioned below the inlet but above maximum water level
- No mechanical components in the backflow prevention path — physically permanent
- Effective even under mains vacuum — no siphonage path exists
- Required for fluid category 5 installations
|
Feature
|
Type AG Air Gap
|
Type AB Air Gap (Cat 5)
|
|---|---|---|
|
Fluid category protection
|
Categories 1–4
|
Category 5 (highest)
|
|
Inlet position
|
Inside tank body at standard lid level
|
In raised housing above tank lid
|
|
Weir overflow
|
Standard overflow in body
|
Weir below inlet, above max water level — in raised housing
|
|
Mechanical components
|
Float valve only
|
Float valve in housing — no backflow valves required
|
|
Backflow mechanism
|
Physical gap between inlet and water surface
|
Permanent physical separation — vacuum-proof
|
|
Prior notification (Reg. 5)
|
Not generally required for Cat 1–4
|
May be required — confirm with water undertaker
|
|
WRAS approval
|
Yes
|
Yes — full assembly including housing
|
|
Tricel range
|
Standard one-piece insulated and uninsulated tanks
|
Category 5 break tanks — one-piece range
|
06
Regulations
Regulations Governing Category 5 Break Tanks
Category 5 break tank installations are governed by a specific regulatory framework. Compliance is mandatory. Failure to comply with the Water Supply (Water Fittings) Regulations 1999 is a criminal offence, with fines and the potential for disconnection of the water supply.
Regulation 3 — WSFR 1999
No waste, undue consumption or contamination
Regulation 3 prohibits the waste, misuse, undue consumption or contamination of water supplied by the water undertaker. Water systems must be designed and maintained so that non-potable water cannot enter the public supply. Category 5 break tanks are a direct response to this requirement.
Regulation 4 — WSFR 1999
Fittings of appropriate quality and standard
Regulation 4 requires all water fittings to be of an appropriate quality and standard and suitable for the purpose for which they are used. WRAS-approved Category 5 break tanks satisfy this requirement for fluid category 5 installations. Non-approved fittings or tanks may constitute a regulatory breach.
Regulation 5 — WSFR 1999
Prior notification to the water undertaker
Certain installations — including those presenting a fluid category 4 or 5 risk — require prior notification to the local water undertaker before works commence. The undertaker has 10 working days to inspect. Failure to notify is a criminal offence. Confirm notification requirements before installation proceeds.
Regulation 31 — WSFR 1999
Backflow prevention by fluid category
Schedule 2 of the Regulations specifies the minimum backflow prevention required for each fluid category. For fluid category 5, a Type AB air gap is mandated. No mechanical device — such as an RPZ valve or double check valve — can substitute for the AB air gap at category 5.
Scottish Water Byelaws 2004
Scotland — technically identical requirements
The Scottish Water Byelaws 2004 are technically identical to the Water Supply (Water Fittings) Regulations 1999 in England and Wales. The same fluid category classifications and backflow prevention requirements apply. Tricel Category 5 break tanks are compliant under both frameworks.
BS EN 1717
European standard — backflow prevention
BS EN 1717 is the British adoption of the European standard for protection against pollution of potable water in water installations. It classifies backflow prevention devices and their applicability by fluid category, providing specifiers with a technical reference for device selection aligned with the Regulations.
Penalties for non-compliance: failure to comply with the Water Supply (Water Fittings) Regulations 1999 is a criminal offence. Penalties include fines starting from £1,000, disconnection of the water supply and court orders. The water undertaker also has the right to inspect any installation and require remedial works at the installer’s expense. Always confirm compliance requirements with the water undertaker before installation.
07
Installation
Installing a Category 5 Break Tank — Key Considerations
Installation of a Cat 5 break tank involves the same physical considerations as any GRP one-piece tank, with additional regulatory steps specific to fluid category 5 installations.
Before installation
Regulatory steps that must precede works
- Confirm the fluid category with the water undertaker or competent inspector — do not self-determine
- Submit prior notification to the water undertaker under Regulation 5 where required
- Allow the 10-working-day inspection window to elapse unless the undertaker confirms acceptance sooner
- Confirm WRAS documentation requirements and obtain the Tricel WRAS certificate reference for submission
Physical installation
Tank positioning and access
- Delivered as a complete moulded unit — confirm access route for the complete tank before ordering
- Note the increased overall height of the raised AB air gap housing above the standard tank lid
- Confirm headroom includes the raised housing height, not just the standard tank body
- Flat, level and load-bearing base required; confirm structural capacity for full water load
- Provide maintenance clearance for access to the weir overflow, float valve housing and tank lid
Connections and commissioning
Pipework and documentation
- Size the inlet mains connection to match the float valve specification confirmed at order stage
- Do not modify the raised housing, weir position or air gap arrangement — modifications may invalidate WRAS approval
- Clean, disinfect and flush the system after installation in line with BS 8558:2015 before returning to service
- Retain WRAS certificate, notification confirmation and commissioning records as part of the building’s asset documentation
Installation of fluid category 5 systems must be carried out by a competent person. Registering with an Approved Contractor Scheme under the Water Fittings Regulations provides the option to self-certify without prior notification. Where installation is not carried out by an approved contractor, Regulation 5 prior notification to the water undertaker applies.
08
Technical Downloads
Category 5 Break Tank Technical Resources
Technical documents for M&E engineers, specifiers, building services consultants and facilities managers. Download for design, specification, procurement and regulatory submissions.
One Piece GRP Tank Product Brochure
Full one-piece tank range including Cat 5 break tanks, standard AG tanks, insulated and uninsulated options.
WRAS Approval Documentation
WRAS approval references for potable cold water storage; required for specification and procurement.
WRAS Approval Documentation
WRAS approval references for potable cold water storage; required for specification and procurement.
09
Specification Support
Specify a Tricel GRP Category 5 Break Tank
The following information is needed to confirm the correct specification for a Category 5 break tank. Confirming the fluid category with the water undertaker before enquiring speeds the process and avoids revision.
Information for a Cat 5 break tank quotation
Fluid category confirmed (water undertaker)
Installation location (internal or external)
Insulated or uninsulated specification
Overall height including raised housing
Incoming mains diameter (float valve size)
Regulation 5 notification — confirmed?
Required storage capacity (litres)
Potable or non-potable duty
Available footprint and headroom
Access route dimensions
WRAS documentation required for project
Pipework and connection positions
Request a Category 5 break tank quote
Tricel’s technical sales team will confirm the appropriate break tank specification, WRAS approval status, size and delivery options for your project.
Where access prevents a standard one-piece tank being positioned, Tricel’s GRP sectional tanks and TIF configurations are available and can also be specified to meet fluid category 5 requirements. Confirm at enquiry stage.
10
Related Products & Resources
One Piece Tank Range & Related Resources
Category 5 break tanks are part of Tricel’s GRP one-piece tank range. The following resources support specification, sizing and compliance across the full range.
11
FAQS
Category 5 Break Tank FAQs
Common questions from M&E engineers, building services consultants, facilities managers and specifiers.
What is a Category 5 break tank?
A Category 5 break tank is a cold water storage tank fitted with a Type AB air gap — a raised float valve housing with a weir overflow — providing the highest level of backflow protection under the Water Supply (Water Fittings) Regulations 1999. Fluid category 5 represents fluids presenting a serious health hazard due to pathogenic organisms, highly toxic or radioactive substances, or faecal, human or animal waste. The AB air gap is non-mechanical: the physical separation between the inlet and the tank water makes mains contamination impossible even under vacuum conditions.
What is fluid category 5?
Fluid category 5 is the highest risk classification under the Water Supply (Water Fittings) Regulations 1999. It describes fluids that represent a serious health hazard because they contain pathogenic organisms, highly toxic substances, radioactive substances, or faecal, animal or human waste. Environments typically generating a category 5 risk include laboratories, mortuaries, veterinary practices, hospitals (clinical areas), agricultural livestock systems, commercial bin stores, car wash facilities, swimming pool plant rooms and industrial chemical handling sites.
What is the difference between an AG air gap and an AB air gap?
A Type AG air gap has the float valve inlet inside the tank body at standard lid level. It provides backflow protection from fluid categories 1 to 4. A Type AB air gap has the inlet mounted in a raised housing above the tank lid, with a weir overflow positioned below the inlet but above the maximum water level. This creates a permanent physical separation that works even under mains vacuum conditions, providing category 5 protection. A standard AG air gap tank cannot be used where a category 5 risk has been identified.
Where are Category 5 break tanks legally required?
Category 5 break tanks are required wherever a mains connection supplies a system presenting a fluid category 5 risk. Common examples include laboratories, mortuaries, veterinary practices, hospital clinical areas, agricultural livestock systems, bin stores, car wash facilities and industrial chemical sites. The fluid category must be confirmed by the water undertaker or a competent person — it cannot be self-determined by the installer or building owner. Regulation 5 of the Water Supply (Water Fittings) Regulations 1999 may also require prior notification to the water undertaker before works begin.
Do I need to notify the water undertaker before installing a Category 5 break tanks?
Under Regulation 5 of the Water Supply (Water Fittings) Regulations 1999, installations involving fluid category 4 or 5 risks require prior notification to the local water undertaker before work begins. The undertaker has 10 working days from notification to inspect or accept the installation. Works begun without the required notification constitute a criminal offence. Where installation is carried out by a person registered under an Approved Contractor Scheme, self-certification without prior notification may be permitted — confirm this with the relevant scheme before proceeding.
Are Tricel Category 5 break tanks WRAS approved?
Yes. Tricel GRP Category 5 break tanks are WRAS approved for fluid category 5 backflow protection. The WRAS approval covers the complete tank assembly, including the raised housing and weir overflow, as manufactured. Confirm WRAS approval status and obtain the certificate reference at the time of order. WRAS documentation is available for inclusion in project O&M manuals and Regulation 5 notification submissions.
Can a Category 5 break tank be used for potable water?
Yes. Tricel GRP Category 5 break tanks are available in insulated form (with CFC-free PU foam) and WRAS approved for potable cold water storage where the full system complies with the Water Supply (Water Fittings) Regulations 1999. The insulated version maintains cold water temperature, supporting Legionella risk management under ACoP L8 and HSG274. Confirm potable duty at the order stage.
Can I retrofit an AB air gap to a standard one-piece tank?
No. The Type AB air gap housing is factory fitted by Tricel during manufacture and forms an integral part of the WRAS-approved tank assembly. It cannot be field-retrofitted to a standard AG tank. Attempting to modify an AG tank to achieve AB air gap performance may invalidate WRAS approval and constitute a regulatory breach. Where a Cat 5 break tank is required, specify the Tricel AB air gap tank from the outset.
What information is needed to specify a Category 5 break tank?
Key information includes: the fluid category confirmed by the water undertaker or competent inspector; required storage capacity; installation location (internal or external); insulated or uninsulated duty; potable or non-potable use; available footprint and headroom (including height for the raised housing above the standard lid level); access route dimensions; incoming mains diameter for float valve sizing; and whether WRAS documentation is needed for submission. Contact Tricel on +44 (0)1934 421 499 or websales@tricelwater.co.uk.
Tricel Water UK - UK GRP Tank Manufacturer
Specify a WRAS-approved GRP Category 5 break tank
Provide the confirmed fluid category, required storage capacity, installation location and any access or compliance requirements. Tricel will confirm the appropriate Cat 5 break tank specification and WRAS documentation.
This product 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.
