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Carat 2700L-6500L Underground Water Tank

£1,238.74£1,848.59 inc VAT

Strong, robust and versatile underground storage tank.


FREE Delivery by Monday, 27 May, 2024.


Protecting you



Versatile Storage Applications: The Carat Underground Water Tank is a highly adaptable underground storage solution designed to hold various substances, including non-potable water, wastewater, raw sewage, effluent, silage, slurry, rainwater, greywater, and bluewater. This capability makes it ideal for a wide range of applications, from residential water management to agricultural and industrial storage needs.

Customisable Size Options: Available in sizes ranging from 2700L to 6500L, the Carat Tank is designed to meet diverse capacity requirements. Whether for small residential properties or larger commercial settings, there’s a Carat Tank to fit every need, ensuring efficient use of space and optimal storage capacity.

Preassembled for Immediate Installation: Delivered fully assembled, Carat Tanks streamline the installation process, saving time and reducing labour costs. This feature ensures that the tank can be quickly and correctly set up, allowing immediate operation upon delivery.

Optional Vehicle Loading Lid: Carat Tanks offer an optional vehicle loading lid to accommodate installations under surfaces such as driveways where space is at a premium. This lid allows the tank to bear significant weight, providing flexibility in tank placement without compromising safety or functionality.

Long-Term Durability with Warranty: Each Carat Underground Water Tank comes with a 10-year warranty, highlighting the manufacturer’s commitment to quality and durability. This extended warranty assures long-term reliability and performance, protecting your investment in critical infrastructure.

Stable in High Groundwater Conditions: Thanks to its robust construction, the Carat Tank’s design ensures stability up to the middle of the tank in high groundwater situations. This feature is critical for preventing water ingress and maintaining structural integrity under challenging environmental conditions.

Adjustable Installation Features: The tank has adjustable lid heights for flush alignment with ground level, accommodating various installation depths and ensuring a neat, discreet finish. Moreover, fully compatible tank domes, risers, and lids address varying invert-level requirements, enhancing adaptability and ease of integration.

Watertight Seal Assurance: All connections between the tank dome, riser, and lid include high-quality thick rubber gaskets, ensuring watertight seals that protect against leaks and environmental contamination.

Flexible Backfill Options: Depending on ground conditions and groundwater levels, Carat Tanks can be backfilled with either granular material or concrete, offering flexibility to meet site-specific requirements and ensure optimal installation integrity.

Choose the Carat Tank for its superior flexibility, reliable performance, and durable construction. It is an excellent choice for managing various storage needs under various environmental conditions.

Images are for illustrative purposes only, there is a possibility that certain products may have been upgraded or replaced with equivalent alternatives.

What’s included

Supplied by Graf

  • Underground water tank & dome (choice of tanks available, sizes vary according to application type).
  • The pedestrian telescopic lid as standard, 3.5 tonnes vehicle loading adjustable lid available on request.
  • Extension pieces (risers) as required (extra over items).

Supplied by Others

  • Inlet/outlet drainage pipework
  • Connecting pipework between multiple tank systems

System Benefits

• Simple & quick to install
• High quality, robust, polypropylene tank & related accessories for use with a wide range of media
• Adjustable lid height for flush alignment to ground level
• Pedestrian telescopic lid as standard, 3.5 tonnes vehicle loading adjustable lid available on request
• Fully compatible tank domes, risers & lids to deal with invert level requirements
• All tank dome, riser & lid connections include a high-quality thick rubber gasket for watertight seals
• Granular or concrete backfill options, subject to ground conditions & groundwater level

Product Dimensions, Levels & Weights

Carat Underground Water Tank Dimensions & Weights (2700L – 6500L)

Carat S 2700L Mini | Download
Carat S 2700L Maxi | Download
Carat S 3750L Mini | Download
Carat S 3570L Maxi | Download
Carat S 4800L Mini | Download
Carat S 4800L Maxi | Download
Carat S 6500L Mini | Download
Carat S 6500L Maxi | Download

CARAT RS-Series Installation and maintenance instructions | Download
CARAT Tank Levels Mini Dome | Download
CARAT Tank Levels Maxi Dome | Download

Mini & Maxi Lid Dimensions

PE Mini Lid (Pedestrian Loading 371010) | Download

PE Maxi Lid (Pedestrian Loading 371011) | Download

Vehicle Loading Lid (371052) | Download

Extension piece options

Extension Sleeve (371003) | Download

Extension Sleeve (371015) 1000mm | Download


Carat Tank (Levels, Maxi Dome) | Download
Carat Tank (Levels, Mini Dome) | Download


Specification Sheet | Download

Installation & Commissioning

This informative guide covers the following:

  • Loading information
  • Tank coverage heights
  • Excavation dimensions
  • Technical & general data
  • Installation & Assembly

Read the Guide | Download

Service Provider Support

Delivery Information

Please note the following regarding Graf UK deliveries

We’re still delivering to our customers safely via our own delivery vehicles & drivers in the main, using external hauliers when required.


This gives us much greater control & flexibility over our deliveries.


All orders are typically delivered within 5-7 working days from receipt of order, however during this time due to UK-wide disruption, some deliveries may take a little longer and we would still aim to deliver within 10 days.


• Delivery lead time is 5-7 working days on all orders, unless otherwise advised.
• Price includes delivery to mainland UK.
• Please check for deliveries into Cornwall, Mid & Northern Scotland & Isles as additional delivery charges may be applicable.
• We cannot currently provide a tracking number for all orders but can accept customer enquiries by phone.
• Off-loading by the customer unless agreed otherwise.
• Tanks are generally strapped to a pallet for fork lift off-load, slings can also be used.
• Please advise if there is restricted access to site or special delivery instructions.