If we’re to tackle the impacts of climate change, we must make water sensitive urban design (WSUD) a legal requirement.

By combining a range of different measures, WSUD captures, stores, uses and slowly dissipates water – reducing flooding and helping to conserve precious water resources. This type of design isn’t just about water management, making the landscape pretty or putting down permeable surfaces to capture water. It’s about health, community spaces, community regeneration (both through physical features and social benefits) and biodiversity. It’s about rising to the real challenge of how we can use that water from the moment it falls on the ground until it’s disposed of, and use it for the benefit of mankind.

Unlocking the environmental, social and economic benefits this can deliver will involve a fundamental change in the way we think about water in our urban landscape – and that’s why it needs to be made a legal planning requirement. As my colleague Vincent Lee wrote recently, water must drive city planning.

In the UK and around the world, climate change is making this challenge increasingly urgent. Climate change is increasing the intensity and frequency of storms. And urban environments containing too much concrete and not enough permeable surfaces exacerbate this problem. As a result, combined sewer systems such as those in the UK (where rainwater is mixed with sewage before treatment) can no longer cope. This risks both flooding and spilling polluted wastewater into watercourses.

Traditional solutions to this problem include increasing the size of sewers or providing extra storage capacity. But these sorts of schemes are expensive, and although they address the immediate problems, they don’t unlock wider benefits in the same way as a water sensitive urban design. Instead, countries with combined sewers need to look at retrofitting a water sensitive design to their existing systems.

Contrary to what you might think, retrofitting in this way is not impossible. But you must start by understanding – and modelling – how water behaves in the catchment area. That’s how we tackled a project in Llanelli with Dwr Cymru Welsh Water, designed to help avoid spilling wastewater into the Loughor estuary and alleviate surface water flooding.

The 20-year delivery plan for the Llanelli project involves measures such as dispersing surface water into parkland to create a feature instead of putting it into sewers. This will achieve the same outcomes as replacing sewers and building storage, but it will also enhance the environment and provide green-space amenities. And it will be at a fraction of the cost.

Other countries – and indeed other parts of the UK – might not get as much rain as Wales or face the same legacy of combined sewer systems, but WSUD is no less important. Water is a precious resource and a water sensitive design can just as easily help to conserve it, especially when you have the luxury of planning a new city from scratch.

As part of Arup’s work on the plan for a low-carbon community in Changxindian, Beijing, we devised a comprehensive water strategy. This incorporates rainwater harvesting, with rainwater collected from roofs across the district and stored in pools underground. Domestic wastewater is also treated and partly recycled for non-potable use.

If more cities around the world are to benefit from WSUD, it must become a planning requirement in new developments. And I think this needs to be backed up on the construction side too, going beyond aspirational ratings like LEED or BREEAM® and becoming part of primary legislation.

Do you agree? I’d be interested to know your thoughts on the way forward.