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The vision is that London will manage its rainwater sustainably to reduce flood risk and improve water scarcity. At the same time maximising the benefits for the people, environment and economy.

What Does The London Sustainable Drainage Action Plan Show?

The London Sustainable Drainage Action plan shows a reduction of surface water flows in the sewer network by 25% until 2040. The aim is to achieve 1% reduction per year over the next 25 years.

This is set to be achieved via Sustainable Urban Drainage techniques such as green roofs and rainwater harvesting etc. The GLA calls for all stakeholders in London to participate.

Flooding Map Of London

Areas highlighted in red on the map above displays where the projected flows in the overall system may exceed its capacity and some flooding should be expected.

How Can Rainwater Harvesting Tie Into The London Sustainable Drainage Action Plan?

Rainwater harvesting is recognised to have an impact not only on reducing mains water consumption but also reducing sewer flows. The GLA acknowledges this in its latest document. Other countries have long taken advantage of the double benefit. For example, Belgium for years has provided a mandatory scheme for all new builds to have combined rainwater harvesting and attenuation systems.

Rainwater harvesting can be a very effective solution, especially in London as the majority of buildings use more water for W/C flushing, in comparison to what can be collected from the roof. This means that zero run off could be achieved in most buildings.

Newest product developments also increase the cost effectiveness of rainwater harvesting systems. The Aqua-Storm-Control system (ASC), is a system based on a cloud technology that uses sensor data, forecast information & modelling to actively control, maintain and monitor water infrastructure such as attenuation or rainwater tanks. Therefore making use of attenuation tanks that would statistically only be used once in a 100 year period.

As the attenuation tank is a requirement and a sunk cost for the building owner/developer, it turns a liability into an asset. The attenuation tank can score BREEAM points and save water as well.

Can I retrofit Rainwater Harvesting?

Rainwater harvesting so far was very difficult to retrofit because drainage pipe work had to be rerouted and spacing for a sizeable tank is required. The ASC is also retrofit-able and can turn existing attenuation tanks into rainwater harvesting systems. The only requirement is the accessibility of the discharge pipe of the attenuation tank and space for a pump set with mains water back-up.

For more information, please see the link for the London Sustainable Urban Drainage Action Plan:

If you would like to find out more, please do not hesitate to get in touch with Lutz Johnen on 0208 991 3725, alternatively you can email us on