A detention cistern collects rainwater and discharges it into the sewer system at a controlled rate. This reduces the burden on drains during periods of peak rainfall. For controlled discharge of the rainwater the detention cistern is fitted with a flow control. This discharges water to the sewer at a rate of 0.5 to 16 litres per second. The water level in the tank rises temporarily during heavy rainfall and falls at the set rate during, and after the rain stops. GRAF detention cisterns are also equipped with an emergency overflow to prevent the tank from overflowing.
You want to install a retention cistern, but don’t want to sacrifice the advantages of rainwater harvesting? The GRAF retention cistern is a combination of rainwater retention and rainwater harvesting. A larger tank is selected according to the requirements, allowing some of the rainwater to be used in addition to the required retention volume.