With COP30 bringing sustainability to the top of the global agenda once more, climate adaptation is, as it so often is, at the centre of discussions. For civil engineers, nowhere is that challenge more tangible than in how we manage water both in terms of water usage and disposal for new developments. Rainfall patterns are increasingly unpredictable, storm events more intense and urban areas more vulnerable to flooding. At the same time, dryer summers and growing water scarcity mean we must also consider how to capture and use water efficiently. This year, the National Standards for Sustainable Drainage Systems (SuDS), published in June 2025, represent significant updates to drainage guidance, reflecting a clear shift in how we approach water management.
The most fundamental change is a shift in mindset: rainwater is now regarded as a valuable resource, not simply a problem to be disposed of. Non-potable water reuse, such as rainwater harvesting, has become the priority for surface water management, signalling that water should be captured and used where possible rather than being rapidly discharged off site. On all new developments, engineers are required to intercept and retain the first 5mm of rainfall, managing the initial runoff at source through appropriate SuDS features. This is more than a technical requirement, it represents a philosophy that places water management at the heart of site design, influencing landscaping, building placement and even how public spaces are configured.
By embedding this approach into every stage of a project, civil engineers are now tasked with considering how water moves across a site, how it can be reused and how it interacts with natural systems, rather than simply channelling it away. It’s a shift that reflects the growing pressures of climate change, urbanisation and extreme weather events, seeing that developments are resilient not only today but over their entire lifespan. In essence, every rainfall event is now an opportunity to manage resources sustainably, reduce flood risk and contribute positively to the environment, a radical change in the way that we used to think about drainage design.
Several other technical changes also have significant implications for design: infiltration systems, such as soakaways or permeable surfaces, must now half-drain within 24 hours of a 1 in 30-year storm, while the overall system must still manage a 1 in 100-year storm event. This is a higher requirement than previous half draining time for the 1 in 10 year storm event and aimed at aligning the requirement to comply with no designed flooding for up to the 1 in 30-year event. The urban creep allowance has been standardised to 10%, reflecting incremental increases in impermeable surfaces that typically occur as sites develop and mature over time.
Additionally, pumped systems now require approval from the SuDS Approving Body or Lead Local Authority, meaning that gravity-based solutions are preferred. While pumps can still be used, reliance on mechanical systems introduces ongoing operational and maintenance considerations, as well as potential points of failure. Designers must therefore carefully evaluate site conditions, layout and future maintenance responsibilities when considering pumped solutions, balancing practicality with compliance and long-term resilience.
One of the more notable changes is that surface water may no longer be discharged into foul sewers, unless the sewer is officially a combined system. On brownfield sites, which often rely on legacy foul connections, this requires designers to rethink drainage layouts and manage runoff on site rather than relying on old infrastructure. While this adds a layer of design consideration, it is a necessary step to improve resilience and protect communities and ecosystems.
Here at CampbellReith we have been exploring what this means in practice. Our team across the offices has been reviewing and sharing thoughts on the CIRIA SuDS Manual to better understand interception techniques and sizing rainwater harvesting tanks on live projects to meet the requirements of the new standards. These exercises have provided valuable insight into design decisions, helping us anticipate challenges and identify solutions that balance runoff control, infiltration and on-site storage.
What most exciting is that this isn’t just about compliance, these changes push us to think more holistically about water as a resource, about resilience in the face of bigger storms and about creating spaces that genuinely respond to the environment and long-term concerns such as drought. The way we are now designing drainage not only influences how a site performs during storm event, but how it now supports the wider community, protects local ecosystems and aligns with the broader sustainability goals.
For civil engineers, this is the new normal of bigger storms, unpredictable rainfall patterns and how every drop of water counts. Embracing these changes isn’t just about meeting the standards it’s about leading the way in how our industry rises to the climate challenge and delivers sustainable development.