The GRAF Retention cistern combines rain retention with rainwater harvesting.

The GRAF retention cistern is a combination of rainwater retention and rainwater harvesting. The detention can be larger if required. In this case, part of the rainwater can also be used in addition to the required detention volume. For example, rainwater can be used for the following applications:

• Watering gardens

• Flushing toilets

• Washing machines

• Cleaning

The use of rainwater means that up to 50 % of drinking water can be saved, and up to 85 % for commercial properties.

The retention cistern is designed such that the rainwater first fills the useage volume. When the useful volume is full, the throttled outflow is activated and the detention volume also becomes available for temporary storage. The detention mechanism with throttled outflow in turn corresponds to a conventional retention system. Following the rainfall event, the position of the outflow prevents the detention cistern from being completely emptied, while the useage volume remains in the tank!


Advantages Carat XL retention cistern:

  • Suitable for HGV loading up to 12 t
  • Dome opening with stainless steel profile for precision fit and secure mounting
  • Can be mounted in groundwater
  • Lower weight than concrete and steel
  • Various connection surfaces DN 100 (4") / 150 (6")
  • Investment security thanks to a 15 year warranty


Volume [l]Length [mm]Width [mm]Height [mm]Weight [kg]order no.add to enquiry

calculated size Request for information

Technical details


max. earth covering [mm] (without groundwater, vehicle loading) 2000


Earth covering with loading capacity [mm] 800 - 2000
max. axle load [t] 8
max. vehicle weight [t] 12

Groundwater installation

Earth covering with groundwater installation [mm] 500 - 1800