Minimax_Optimax Filter
overflow syphon odour prevention
floating intake vavle
carat indirect system schematic

Carat In-Direct Rainwater Harvesting System 2700-6500 Litres

£2,834.87£3,468.10 inc VAT

The Indirect-supply system collects rainwater for toilets, washing machines, irrigation, and outdoor cleaning. It uses a filter and a pressure-sensitive pump in an underground tank. When a valve is opened, water is pumped under pressure and gravity-fed from a header tank to fulfill water demands. The system automatically switches to mains water when rainwater is insufficient, and a floating ball valve controls the top-up. For garden irrigation, an outside tap can be connected directly to the pump for pump pressure supply.


FREE Delivery by Monday, 03 June, 2024.


Protecting you


How does the Carat In-Direct Rainwater Harvesting System work?

The indirect supply system is designed to support WCs, washing machines, irrigation, and outside cleaning purposes. Rainwater is collected from the roof of the property and fed into the underground tank via the downpipes. On entry to the tank, the water passes through a filter to prevent any debris from going into the tank. With this system, there is a pressure-sensitive pump located in the underground tank. When a valve or tap is opened, water will be pumped under pressure until the valve is closed, allowing the system to repressurise turning the power off to the pump. From the header tank, the water is gravity-fed to the WC’s, etc.

It is all automatic; whenever there is a demand for water, i.e., when the toilet is flushed, the harvested rainwater will be gravity fed to the toilet from the header tank, and then the header tank is topped up by the pump inside the underground tank. In periods without rainfall, the water level inside the underground tank will drop. When the rainwater level is too low, the pump will stop pumping harvested rainwater to the header tank. This, in turn, will result in the rainwater level in the header tank dropping. Inside the header tank, there is a floating ball valve that controls the top-up of mains water in periods with no rain. This means that the system maximises the use of all available rainwater.

If the system is to be used for garden irrigation, an outside tap should be installed on the pipework directly off the pump. A T-junction can be used to achieve this. This will imply that direct pump pressure is now supplying the garden tap. (NB: when the tank is low on rainwater, there will be no mains water top-up to the outside tap.)


Why choose the Carat In-Direct Rainwater Harvesting Package?

  • Innovative Gravel Backfill: Our system uses gravel backfill, significantly reducing installation costs by £60 per cubic metre compared to concrete.
  • Adaptable Installation with Vehicle Loading Lid: Space constraints? The vehicle loading lid allows for installation under driveways, maximising space and utility.
  • Environmentally Responsible Design: The underground tank is made from 100% recycled plastic, showcasing our commitment to sustainability.
  • European Market Leader Quality: Trust in a product renowned for its reliability and effectiveness in rainwater harvesting.
  • Efficient Water Management: Equipped with an automatic submersible pump featuring automatic restart and dry-run protection, it ensures smooth and low-maintenance operation.
  • Consistent Water Supply: The system includes an integrated mains water back-up, which automatically tops up the header tank with mains water when rainwater levels are low, guaranteeing a continual water supply.

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 tank (choice of tanks available, sizes vary according to property type)
  • Telescopic lid (choice of telescopic lid available, depending on tank location)
  • Minimax filter supplied in accordance with type of tank
  • Submersible pump with floating water intake
  • Float switch (connected from mains water backup unit to the underground tank)
  • Header tank package

Supplied by others

  • 100mm diameter duct pipe to contain; float sensor cable, power cable for pump, also bringing mains water to underground tank as and when required
  • 100mm diameter drainage pipe connected from downpipes to the inlet at the top of the tank (all downpipes brought into one pipe for connection to the filter)
  • 100mm diameter pipe for overflow from the tank to mains drainage network

System Benefits

  • Simple & quick to install
  • Submersible pump supplies harvested rainwater on demand to the header tank where it is then gravity-fed to the WCs & washing machine
  • The header tank controls the operation of the system
  • Dual valve system within the header tank prioritises rainwater supply over mains water, maximising the use of all available rainwater to save on mains water consumption
  • Mains water switchover point is at a lower level in the header tank and becomes operational when rainwater is not available from the underground Carat tank
  • Mains water backup supply is not reliant on power supply or pump pressure and therefore guarantees supply of water to WCs at all times

Product Dimensions, Levels & Weights

Carat 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



GRAF Carat S RWH Brochure | Download

Data Sheets

Carat House In-Direct Package | Download


Carat Indirect Schematic Layout | 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
Read the Guide (Tank Only) | Download

Service Provider Support

Graf UK has a national service provider network of contractors who can offer various services including the installation of our tank systems.

Coming Soon: New UK map with the service provider/installer contact details.

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 forklift off-load, slings can also be used.
• Please advise if there is restricted access to the site or special delivery instructions.

Additional Items