Question to the Department for Environment, Food and Rural Affairs:

To ask the Secretary of State for Environment, Food and Rural Affairs, what comparative assessment his Department has made of the cost of (a) using sustainable urban drainage systems to manage rainwater on site of new developments and (b) allowing this rainwater to flow into sewers.

Comparative and impact assessments of the type requested are not currently available. This is primarily because the design of Sustainable drainage systems (SuDS) for any given development site will depend on a range of factors, including topography of the site, development size, development type, and rainfall rates.

SuDS provide a range of benefits. They mimic natural water flow and are designed to reduce the impact of rainfall by using features such as soakaways, grassed areas, permeable surfaces and wetlands. This reduces the pressure on our drainage infrastructure by reducing the quantity of water that ends up in the sewers and storm overflow discharges, mitigating flood risk and preventing pollution from untreated sewage ending up in our waterways.

SuDS also improve the quality of water entering our drainage infrastructure as they offer a natural filtration process, thereby removing pollutants. SuDS provide additional benefits, such as boosting biodiversity, improving local amenities, harvesting rainwater for reuse, heat island mitigation, improve air quality and even providing food growing opportunities.