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Brief Overview

  • Rainwater is collected from the roof area.
  • Leaves and other debris are removed via a pre-tank filter.
  • Rainwater enters the rainwater storage tank via a calmed inlet.
  • The rainwater tank is connected to attenuation crates.
  • Our intelligent control panel will ensure 100% of capacity is always available by monitoring future weather patterns.
  • If required, our control panel will open a valve to reduce the level of stored rainwater.
  • When a demand is detected, submersible pumps draw rainwater through a floating suction filter.
  • The system control panel controls an automatic mains water backup.
  • Rainwater is boosted to points of use including toilets, irrigation, vehicle wash down, and cooling.

Technical Explanation

 rainwater being collected from a commercial roof space for reuse on a rainwater harvesting system


Rainwater is collected from the roof area of the building via roof drainage points.

Roof areas offer the cleanest collection surface for reusing rainwater. Collecting rainwater from paved or hardstanding areas requires much more treatment, increasing maintenance complexities and costs.

Large buildings often use siphonic drainage to effectively remove rainwater from the roof. This method of roof drainage generates higher flow rates than traditional gravity-fed drainage. These higher flow rates must be reduced before the preliminary filtration in the Active Attenuation System.

 pre-tank filtration on a rainwater harvesting system

Preliminary Filtration

Rainwater collected from the roof area is sent through a pre-tank filter, located before the main storage tank. Pre-tank filters are designed to remove undissolved solids from the rainwater supply and prevent them from entering the main storage tank.

Leaves, bird debris, and other organic matter are all filtered out during this stage of filtration. Pre-tank filters work by passing rainwater through a mesh sheet of metal. Any remaining debris is collected on the surface of the mesh allowing clear rainwater into the tank.

Pre-tank filters must be easily accessible for maintenance as the filter will require regular cleaning to remove debris, even if the pre-tank filter includes a backwash spray.

Pre-tank filters should also be rated to 1000 microns (1mm).

 Combined rainwater harvesting and attenuation storage

Attenuation Storage

Storage on a combined rainwater harvesting and attenuation system differs slightly from standalone systems.

Attenuation capacity is split into two. Half of the attenuation capacity holds rainwater from the roof area only. The remaining attenuation capacity is for surface water from car parks and paved areas.

Rainwater from the roof area is best suited for reuse as it is relatively free of debris and contaminants, unlike rainwater from car parks which contain hydrocarbons. While it is possible, removing surface-related contaminants from the rainwater supply can be costly and maintenance-intensive.

The two capacities should be connected via a high-level overflow with a non-return valve to prevent cross-contamination.

 rainwater storage tank in a combined rainwater harvesting and attenuation system

Rainwater Storage 

A small rainwater harvesting tank is connected to the roof attenuation capacity. The storage tank and roof attenuation are connected via a low-level balancing pipe.

The rainwater harvesting tank acts as a pumping chamber to boost rainwater into the building. The tank also contains the necessary pre-tank filter with suitable maintenance access for debris removal.

The rainwater storage tank is located at a slightly lower level than the attenuation capacity, ensuring the attenuation always drains down into the rainwater tank.

 the stormwater valve on a rainwater harvesting and attenuation system

Control Valve

Our intelligent control panel links with Met Office weather forecasting data to determine the safe level of stored water via a level sensor.

If required, our intelligent control panel will temporarily open the valve to release the necessary volume of stored water into external drains, minimising pressure on infrastructure by releasing stored water before heavy rainfall arrives.

Our intelligent controller completes a regular communications test with the weather data to ensure the connection is active. If no signal is detected, the system will default to a standard attenuation system and the valve will automatically open.

Where the storm valve is located at a lower level than on-site drainage, for example in a basement, our intelligent control panel can work with a booster set to pump stored water up to the required level to drain.

 rainwater harvesting system supplying toilets

Usage Points

Rainwater can be used to supply

  • Toilets
  • Irrigation systems
  • Vehicle and train wash
  • Manufacturing processes
  • Dust suppression
  • Cooling

Rainwater cannot be used to supply

  • Potable outlets
  • Showers

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