Episode 191 - New Sustainable Drainage Systems Standards

This week we will be talking about  the new National Standards for Sustainable Drainage Systems recently published for use in England and applicable to new developments.. This episode content meets PC3 - Legal Framework & Processes of the Part 3 Criteria.

Resources from today's episode:

Websites:

• https://www.riba.org/work/insights-and-resources/professional-features/what-do-architects-need-to-know-the-new-national-standards-for-suds/
• https://www.gov.uk/government/publications/national-standards-for-sustainable-drainage-systems/national-standards-for-sustainable-drainage-systems-suds#standard-1-runoff-destinations

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Transcript

Episode 191:

Hello and Welcome to the Part3 with me podcast. 

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I am your host Maria Skoutari and this week we will be talking about the new National Standards for Sustainable Drainage Systems recently published for use in England and applicable to new developments.Todays’ episode meets PC3 of the Part 3 Criteria.

In today’s episode we’ll break down what the standards cover, why they matter for architectural practice, and exactly what as architects we need to know to design compliant, sustainable schemes.

Let’s start with the basics, what do we mean by Sustainable Drainage Systems and why do they matter: 

Sustainable Drainage Systems are methods designed to manage surface water runoff in a way that mimics natural drainage, helps prevent flooding, improves water quality, and creates amenity and biodiversity benefits. Historically, developments managed water through underground pipes, channeling runoff away from the site as quickly as possible. The new standards call for a radical change. Instead, architects and engineers must work with the concept of a “SuDS Approach”—designing surface water systems that treat rainfall and runoff as resources and keep them on-site wherever feasible.

Sustainable Drainage Systems are integral to contemporary best practice for environmental protection, urban resilience, and compliance with planning regulations. Their role is increasing with climate change driving heavier and less predictable rainfall events. Regulations and standards are now putting robust frameworks around how, where, and why Sustainable Drainage Systems should be implemented on new development sites rather than retrofitted, though retrofit opportunities do exist in principle. The need for their implementation to mitigate flooding impact was first outlined in the 2010 Flood and Water Management Act and was set to become mandatory and adopted by the SuDS Approving Body, however this was implemented in Wales and partially in Scotland but not England. Instead, a reduced technical standard, focused primarily on hydrology and mitigation of flood risk and omitting any wider architectural and landscape design considerations, was produced by Defra in 2015. A subsequent government review of Schedule 3  of the 2010 Flood and Water Management Act and a recommendation to make SuDS mandatory for all housing development in England by 2024 was not taken forward. The new National Standards now released replace the 2015 standard with a far more comprehensive set of guidelines, similar to those in Wales, that goes a long way towards promoting better outcomes from Sustainable Drainage Systems delivered as part of new developments.

Who are the New Standards for:

The standards apply to architects, landscape architects, engineers, developers, planning authorities, and any party involved in the design and delivery of new infrastructure and development in England. Whether working with greenfield sites (undeveloped land) or brownfield sites (previously developed), professionals need to adhere to these new standards, which set minimum design and operational requirements, outline hierarchical principles for runoff destinations, and set the scene for joined-up, multi-benefit surface water management.

It’s worth noting these standards apply only to management of essentially uncontaminated surface water runoff. For higher-risk land uses, such as, large car parks where risk of pollution escalates, additional proprietary measures and potential engagement with the Environment Agency may be necessary.

So what do the new Standards consist of:

The new document published by the government in July 2025, sets out a suite of seven interlinked standards. These are split between one "hierarchy standard"—Standard 1, which deals with prioritising final runoff destinations—and six fixed standards covering design and operational minimums.

The standards consist of:

• Standard 1: runoff destinations
• Standard 2: management of everyday rainfall (interceptional)
• Standard 3: management of extreme rainfall flooding
• Standard 4: water quality
• Standard 5: amenity
• Standard 6: biodiversity
• Standard 7: design of drainage for construction, operation, maintenance, decommissioning and structural integrity

Each standard is supported by requirements and explanatory notes. The wording differentiates between statutory requirements (“must”), performance-based standards (“shall”), recommendations (“should”), permissible approaches (“may”), and factual notes (“can”).

The standards operate synergistically, meaning each helps deliver the goals of the others. So, a robust surface water system might support water quality, enhance biodiversity, provide amenity, and manage flood risk all at once.

The new standards embed several core principles. The first principle requires that drainage systems be designed, constructed, operated, and maintained using a natural approach—mimicking natural drainage as closely as possible and managing flow at or close to the surface, as near to the source as practicable. This contrasts with the legacy of piped drainage. Surface water should be harnessed as a resource on site and provide broad benefits—helping with climate resilience, supporting biodiversity, contributing to water supply, and protecting receiving waters from pollution. The design ought to be multifunctional, meaning drainage features should serve as parts of landscaping, amenity spaces, or points of biodiversity enrichment.

Another key principle states that surface water management must be considered from the very earliest stage of site appraisal and design. Architects should integrate Sustainable Drainage Systems with site topography, existing hydrology, land contamination strategies, roads and public spaces, and the wider strategy for biodiversity and climate resilience. The standards call for early engagement with planning authorities, aligning with local flood management strategies and securing relevant consents right at the start.

Crucially, compliance with Sustainable Drainage Systems must be demonstrated throughout the planning application process and integrated within the site’s development and landscape design—showing, phase by phase, how runoff will be managed.

Now, let’s look at each standard in a little more detail. Starting with Standard 1—Runoff Destinations:

The first of the National Standards is central. It sets out a strict hierarchy for runoff destinations and mandates that runoff from developments must be discharged to the highest priority available, maximising sustainability and minimising environmental harm.

The hierarchy looks at:

• Firstly, collected for non-potable use (rainwater harvesting)
• Then run-off, infiltrated to ground (using infiltration methods)
• Discharged to above-ground surface water bodies (such as rivers, lakes)
• Discharged to surface water sewers or piped drainage
• Discharged to combined sewers (lowest priority, most environmentally problematic)

The rationale is that the further up the hierarchy, the closer you keep water as a resource, reduce environmental impact, and minimise the risk of flood or pollution. To use a lower-priority destination (for example, a combined sewer), evidence must be provided that all higher-priority options have been exhausted—too expensive alone will not be accepted as a justification to not adopt a certain option.

Standard 1 also includes guidance around obtaining required easements for discharge, especially across third-party land, risk assessment for flooding and pollution, and ensuring that runoff does not deplete surface water or groundwater below safe levels. Rainwater harvesting is mandated for circumstances with demand for non-potable water—such as irrigation or where properties are in areas of water stress. Such systems will need to be designed in accord with relevant British Standards.

Where infiltration is proposed, ground conditions must be suitable and infiltration rates verified by proper assessment. The base of infiltration features must be clear of maximum groundwater levels, and stability of ground and riverbanks must be protected. Any attempt to discharge to certain destinations will require written agreement from the risk management authority, confirming sufficient capacity and compliance with discharge parameters.

If the use of mechanical pumping for surface water is explored, it will only be accepted by exception  and permitted if gravity drainage cannot be achieved. It must also be agreed with the approving body, taking carbon, energy, and maintenance into account.

So that provides a brief overview of Standard 1, let’s move on to Standard 2 of the ‘fixed’ standards covering Managing Everyday Rainfall (Interception):

This standard asks designers to apply the Sustainable Drainage Systems approach to ensure the first 5mm of rainfall for most events does not result in runoff to surface water or piped systems. The goal is to intercept “everyday” rainfall—non-extreme events—and use features like green roofs, rain gardens, rainwater harvesting systems, permeable surfaces, swales, infiltration trenches, and ponds to keep water on-site whenever possible. Evidence will be required that this everyday rainfall is either used, infiltrated, or absorbed within Sustainable Drainage System features and that they deliver amenity and biodiversity benefits. Robust calculations and demonstration of interception will be key for planning consent.

Next, moving onto Standard 3: Management of Extreme Rainfall and Flooding:

Under this standard, Sustainable Drainage Systems must be sized to handle extreme events, protect people and property, allow for climate change and “urban creep” leading to future increase in impermeable area, and ensure runoff rates do not increase flood risk elsewhere. There are strict controls for allowable discharge rates, strict flood protection parameters, and requirements to account for adjacent sites’ flood risk. Flooding within outfall design or attenuation zones must be shallow, low-risk, and temporary. As part of the implementation of this standard, geotechnical investigations will be required to confirm infiltration suitability and inform calculations.

Then, under Standard 4: Management of Surface Water Quality:

This standard, requires that development runoff must not cause pollution to groundwater or surface water bodies. Sustainable Drainage Systems design is geared not only to manage water quantity but also water quality, controlling the transport of contaminants and particulates by including features such as vegetated swales, filtration zones, or engineered interventions. As such, proposed Sustainable Drainage Systems will be based on a robust water quality risk assessment appropriate to the pollution hazard and sensitivity of receiving waters.

Now relating to Standards 5, 6 & 7: These explore Amenity, Biodiversity, and Design of drainage for construction, operation, maintenance, decommissioning and structural integrity:

Whereby Sustainable Drainage Systems must deliver amenity benefits, enhance biodiversity, be maintainable, and prove durable for the lifetime of the development. Architects are encouraged to work with landscape professionals, ecologists, and end-users in such occasions in order to incorporate the numerous benefits that can be achieved by utilising drainage design contributing to place-making, recreation, climate resilience, and wildlife support.

Maintenance strategies must be designed-in from the start, with clarity around who is responsible for ongoing management and with features that support easy inspection, operation, and replacement as needed. Designers will be required to provide a management and maintenance plan supporting design objectives ensuring the performance of the surface water drainage system with regards to runoff destinations, everyday and extreme rainfall, water quality, amenity and biodiversity is maintained throughout the lifetime of the development. Surface water drainage design shall examine for the likelihood and consequences of potential failure scenarios that may occur during the operation phase and safely manage the associated risks and shall be designed to ensure structural integrity of all components under anticipated loading conditions for the design life of the development so that it does not affect the structural integrity of any existing or proposed components within, or adjacent to, the development.

To support these standards, Section H3 of Approved Document H (Drainage and waste disposal) of the Building Regulations 2010 provides guidance on meeting the technical requirements of surface water drainage for buildings and the surrounding areas. First and foremost of course, surface water drainage system proposals will need to meet Building Regulations.

It is fundamental that arrangements are put in place for the future maintenance of Sustainable Drainage Systems features. Where they serve a single property, such as a dwelling, business or retail complex, maintenance will remain the responsibility of the property owner, unless another appropriate body is to adopt the Sustainable Drainage Systems features. For surface water drainage systems serving more than one property, an appropriate body will need to adopt and be responsible for the maintenance of the Sustainable Drainage System features and ensure that they continue to comply with the national standards. To be adopted by an appropriate body, the surface water drainage system shall be designed, constructed and function as approved in accordance with the national standards.

So how should architects start to adopt these standards and what does it mean for their proposals and clients: 

Moving forward, architects will need to integrate Sustainable Drainage Systems (SuDS) from the earliest stages of their projects. Early consideration of Sustainable Drainage Systems can have far-reaching effects on site layouts, the orientation and positioning of buildings, the configuration of public spaces, and the overall landscape treatment. By embedding these systems at the conceptual phase, architects can ensure that Sustainable Drainage Systems solutions are both functional and harmoniously integrated with wider site and architectural objectives.

Collaboration will be key; it is essential that architects engage with engineers, landscape architects, local authorities, and water management professionals right from the outset. This interdisciplinary approach supports smoother project delivery by ensuring that technical requirements, local guidance, and regulatory expectations around Sustainable Drainage Systems are met without late-stage compromise or costly redesigns.

Throughout the planning process, architectural teams will increasingly be required to provide robust evidence demonstrating compliance with Sustainable Drainage System standards. This evidence must be visible across all planning submissions, including design drawings, technical reports, detailed specifications, and long-term maintenance strategies. Aligning these documents not only satisfies statutory requirements but also builds confidence among stakeholders that the scheme’s drainage solutions will perform as intended.

A strong working knowledge of relevant British Standards—such as BS EN 16941 for rainwater harvesting—alongside current Environment Agency guidance and local authority Sustainable Drainage System policies, will be fundamental to producing compliant and effective design proposals. Architects must continue to develop this knowledge to ensure that their designs are both innovative and fully aligned with statutory and best practice requirements.

Ongoing responsibilities for maintenance, adoption, and operational handover will also fall within the architect’s remit, especially as Sustainable Drainage System features become more integral to the function and appearance of developments. Understanding these responsibilities ensures the long-term success and resilience of drainage systems and minimises the risk of operational failure or future liability.

While Sustainable Drainage Systems bring new creative possibilities for place-making and sustainability, they also introduce technical challenges that architects must navigate. These challenges include dealing with difficult ground conditions for infiltration, diagnosing and mitigating issues related to contaminated land, securing rights and easements over third-party property, and reconciling creative ambitions with firm regulatory standards. Architects must also consider the technical feasibility of connecting to downstream systems, securing agreement from authorities on capacity, and ensuring robust plans for funding and maintaining Sustainable Drainage Systems, especially in complex or multi-owner schemes. At the same time, compliance with Sustainable Drainage Systems delivers opportunities: enhancing site biodiversity, improving visual and environmental amenity, supporting climate resilience strategies, accelerating planning approvals, and lowering long-term operational risks and costs for clients.

To succeed in this evolving regulatory landscape, architects should actively build their awareness and understanding of the Sustainable Drainage Systems hierarchy and specific standards. Developing skills in early-stage design, with focused attention on surface water management, is now essential. Equally, prioritising evidence-led design—demonstrating at every project stage how Sustainable Drainage System standards are met—will be critical. Building strong relationships with local authorities, landscape professionals, and engineers will underpin successful project delivery. Adopting a “maintenance mindset,” wherein design choices facilitate ease of ongoing operation, will safeguard the function of these drainage systems across the building’s lifecycle. 

To sum up what I discussed today:

• Sustainable Drainage Systems (SuDS) are now central to best practice—managing surface water sustainably, enhancing biodiversity, and building climate resilience through designs that mimic natural drainage.
• The 2025 National Standards replace the limited 2015 version with a comprehensive, seven-part framework that integrates hydrology, water quality, amenity, biodiversity, and long-term maintenance principles.
• Architects must integrate Sustainable Drainage Systems from the earliest design stages, aligning proposals with site topography, planning policy, and the new national hierarchy that prioritises rainwater harvesting, infiltration, and reuse over discharge.
• Collaboration between architects, engineers, landscape designers, and authorities is essential to achieve compliant, efficient, and multifunctional drainage designs that add tangible value to developments.
• Maintaining Sustainable Drainage Systems over the lifetime of a project is now as critical as their design—requiring clear adoption routes, defined responsibilities, and evidence-based strategies to ensure performance, resilience, and long-term sustainability.