At Welsh Water, we are leading the way in developing and using new, innovative solutions to manage the amount of surface water entering our sewers. We have called this approach RainScape.

We plan to invest more and more in RainScape, around £80 million up to 2020.

This will help to reduce the risk of sewer flooding and pollution, whilst also helping to increasing capacity in our sewer network. It will also help to support economic development and protect our customers against climate change.

What’s the problem?

For the most part, our sewers are a single pipe that has to cope with both surface water and foul water from our properties. This means that during periods of heavy rainfall, more water is getting into our network than it can cope with, increasing the risk of sewage flooding. Resolving this problem using traditional methods such as building additional storage tanks and pipes is expensive and not sustainable. Neither does it tackle the root cause of too much water getting into the sewers.

The RainScape schemes we have developed reduce the surface water entering our sewers and where possible catch, redirect and slow down the speed at which surface water enters the sewer network, using a range of techniques that we call ‘RainScape solutions’.

What’s the solution?

Having learned from the international examples of surface water schemes in Malmö, (Sweden) and Portland (Oregon, USA). We have created our own range of surface water solutions that we call RainScape solutions. These solutions can be incorporated into new developments, or installed into the existing sewer systems. They include:

  • Basins and Planters: Shallow landscaped basins that capture the surface water runoff from roofs and road and store and treat the surface water. The water filters through the plants within the basin, removing contaminants before being released into the soil or the sewer network. These can be small, and fitted to individual downpipes, or they can be larger, and used within road schemes.
  • Swales: Long, shallow, landscaped channels that reduce the speed of surface water - cleaning it and where possible allowing it to gradually infiltrate into the soil. Where it is not possible for the water to infiltrate the water into the ground, the swales gradually return the water into the sewer network at a slower rate.
  • Porous paving: Paving that is designed to allow surface water to pass through it, rather than over it into nearby drains. Porous paving comes in a variety of appealing designs.
  • Filter strip: Filter strips are strips of ground where water running off a site can pass through it, allowing some or all of it to soak away. The rest often enters a swale or another sustainable urban drainage system.
  • Grass channels: These are strips of grass that can be installed in side streets and back alleys of terraces to provide a permeable surface for water to soak through.
  • Geocellular storage: Geocellular systems can be used to control and manage surface water runoff either as a soakaway or as a storage tank. These can be installed beneath roads and kerbs and help to reduce the speed at which surface water enters the sewer network.


  • Local environments will become more attractive and new habitats will be created
  • Reduces the risk of sewer flooding
  • More sustainable and cheaper than traditional methods – helping us to keep customer bills low
  • Helps our communities to become more resilient to climate change

Greener Grangetown - Sharing our learning

In an effort to share our learning and exchange best practice, we held a seminar in March 2013 featuring world renowned environmentalist, Tony Wong (Chief Executive Officer of the Cooperative Research Centre for Water Sensitive Cities in Melbourne). This was held jointly with the former Environment Agency, Cardiff Council and CIRIA.

This was an opportunity to launch a feasibility project ‘Greener Grangetown’, which is a jointly funded project between ourselves and Cardiff Council and will look at creating a number of community focused green streets which feature ‘pocket parks’ in the Grangetown area of Cardiff. This will drastically reduce the surface water runoff from the area whilst also enhancing the aesthetic, and we hope property value of the area for our customers. The removal of this water will reduce our pumping and energy cost overheads as well as creating headroom for tens of thousands of new properties and commercial premises to support the growth of the Welsh capital.

Tony Wong has commended our approach, which can be viewed on this video:

Involving you

We want to involve our customers in the design of our RainScape schemes. We will be holding drop-in sessions with customers that live near to our future schemes. There will be the opportunity at these sessions for you to have your say and to help shape our plans.

For more information, you can email: rainscape@dwrcymru.com

For more information on what you can do to help, visit this page.