1000 Gallon Underground Rainwater Tank for Residential and Commercial Use
If you’re looking for a long-lasting, high-performance underground rainwater collection tank, the Graf Carat S 1000 Gallon Cistern delivers unmatched reliability. With a patented design that allows it to remain stable even when empty, this underground water tank is perfect for rainwater harvesting in both residential and commercial settings. It's groundwater-stable, frost-proof, and includes a locking, childproof PE lid, making it one of the most trusted water storage tanks in the world.
Whether you're managing water for irrigation, toilets, or graywater systems, this tank is engineered to make your system efficient, scalable, and built to last.
Features and Benefits of the Graf Carat S 1000 Gallon Cistern
✓ Guaranteed Stability When Empty – Unlike many cisterns, this rainwater tank won’t collapse when drained, as long as it's installed correctly per manufacturer guidelines.
✓ Fast, Tool-Free Assembly – Patented quick-connect design with no screws required; easy to install and just as easy to disassemble.
✓ Riser and Locking Lid Included – Comes standard with a 14" telescopic riser and childproof PE lid that adjusts to surface level and tilts up to 5°.
✓ Expandable and Future-Proof – Modular design makes it easy to expand your rainwater harvesting system later without replacing the tank.
✓ Groundwater-Stable Design – Can be buried 30" to 42" deep (standard), or up to 70.9" deep with optional risers — even in areas with high groundwater.
✓ Safe, Clean Water Collection – Multiple integrated seals block dirt and prevent seepage contamination, keeping your rainwater pure and usable.
✓ Vehicle-Loading Option Available – Upgrade to a car-bearing configuration to allow driveway or parking lot installations.
✓ Made from Recyclable Duralene – Engineered for long life and sustainability with TÜV safety certification and a 15-year manufacturer warranty.
The Tank Guaranteed Not to Collapse When Empty*
- 1000 Fully-usable gallons
- Attractive Riser and Locking Lid Included
- Car-bearing Option Available
- Groundwater stable up to the top of the tank (below the dome and riser)
* When installed in compliance with manufacturer's installation instructions
Easy and safe assembly
- The patented quick connection (illustrated in green), allows the Carat tank to be assembled without screws in only few minutes. Disassembly is possible at any time.
- The first-class EPDM material used in the profile seals (illustrated in yellow), has been laboratory tested to last more than 25 years.
- The centering bolt (illustrated in orange) assures the accurate and easy assembly of the two half shells preventing any leaks
More advantages
- Variable burial depth: 30" to 42" in standard configuration even in groundwater up to the top of the tank
- 70.9" maximum burial depth even in groundwater up to the middle of the tank using optional risers
- Unique in the world! – a global innovation: unique manufacturing process produces the highest stability due to latest techniques
- Unique fit accuracy of the components thanks to new production process
- Consistent quality due to TÜV safety testing and production monitoring
- Vehicle-bearing (with telescopic cast iron manway kit)
- Groundwater stable up to the middle of the tank due to extremely rigid construction
- Secure investment with market leading 15-year warranty
- Made from high quality Duralene; easy to recycle
- Can be expanded as required
- 26" Manway opening
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Flush with ground level (2 seals) |
| The Carat S underground tank has numerous seals to effectively stop dirt getting into the tank. This means that seepage water cannot get into the tank and, thus, dirt particles cannot contaminate the rainwater. The seals are in the intersection between the tank and the tank dome and between the tank dome and the telescopic dome shaft. All supply pipes connected to the tank dome are also sealed with five lip seals as standard. |
Application
- The global innovation – the new tank generation of the Carat rainwater underground tanks have been specially developed for rainwater harvesting
- Frost-proof installation underground
- Groundwater stable up to the middle of the tank due to extremely rigid construction
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The tank that turns its head for you
The GRAF Carat S underground tank has a rotating tank dome. The tank dome can be aligned with the connections independently of the tank – this makes installation much easier! All installation pipes are connected using the five standard lip seals. The Carat S telescopic dome shaft connects the system to the ground surface. The height of the tank can be smoothly adjusted to suit the local conditions and it can be tilted by 5°. The whole system is flush with ground level.
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Logistical advantages of the Carat
The Carat tank consists of two half shells which can be stacked on top of each other, allowing multiple tanks to be stacked on a single pallet for shipping. For example, it is possible to stack seven 1,000 gallon Carat tanks on a single pallet. This allows a standard 40 ft. shipping container to house a total tank volume of up to 34,000 gallons! The tanks' unique stacking feature directly reduces transport costs and environmental impact from vehicle emissions.
Available Options
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Optional Optimax Pro® Internal Filter Package
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Includes Optimax Pro Internal filter kit with calming inlet, overflow siphon, spannfix connection sleeve and downpipe.
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| Vehicle Loading Option |
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Includes heavy duty telescopic dome shaft and cast iron lid for vehicle loading up to a maximum axle loading of 2.2 tons.
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Manuals and Warranty
Warranty: 15-Year Manufacturer Guarantee when installed as directed.
