National Standards for Sustainable Drainage Systems (SuDS) 2025

• Shift to Formal Standards: SuDS are no longer just ‘good practice’ guided by policy; they are now defined by a clear set of seven national standards, increasing expectations for compliance and consistency.
• Runoff Hierarchy is Mandatory: Developers must now follow a strict hierarchy for discharging runoff, prioritising on-site reuse and infiltration. Deviating from this requires robust evidence.
• Greater Technical Rigour: New, specific design criteria for flood risk—including storm event caps (1-in-2 and 1-in-100 year) and a 10% urban creep factor—demand more detailed hydraulic modelling and design.
• Green Infrastructure is Central: Amenity and biodiversity are now formal standards, requiring SuDS to be designed as multi-functional spaces that deliver measurable environmental net gain, not just as drainage assets.
• Whole-Lifecycle Focus: A major emphasis is placed on long-term performance, with mandatory requirements for detailed maintenance plans, construction method statements, and designing for structural durability.

There are two types of standards:

• Standard 1 is a hierarchy standard and gives the criteria for prioritising the choice of final runoff destination. 
• Standards 2-7 are fixed standards, which state the minimum design criteria of all surface water drainage systems, including how they should be built, maintained and operated.

Standard 1: runoff destinations

This standard sets the priority for where water runoff should be discharged. The hierarchy is: ↓ Collected for non-potable use e.g. rainwater harvesting (e.g. toilet flushing, irrigation) 

↓ Infiltrated to the ground. 

↓ Discharged to an above-ground surface water body. 

↓ Discharged to a surface water sewer or another piped drainage system. 

↓ Discharged to a combined sewer.

Developers should provide evidence to justify using lower-priority discharge locations.

Standard 2: management of everyday rainfall (interception)

For most rainfall events, the first 5mm of rainfall must be intercepted within the development. This applies to both winter and summer seasons and is designed to manage frequent, small-scale rainfall.

Standard 3: management of extreme rainfall and flooding

This standard sets out the requirements for designing infiltration features and the allowable discharge rates to surface water features or sewers during heavy rainfall events. For example the surface water runoff rate for the 50% AEP  (1 in 2 year) event shall be controlled to ensure development runoff from an event of this magnitude has no negative impact. For the 1% AEP (1-in-100 year) storm events and applying a 10% urban creep factor for developments with curtilage. Any flooding from off-site sources for the 1% AEP event should be managed on site or safely routed through the site, ensuring any downstream risks are not increased compared to the pre-development scenario. This is to mitigate flood risk.

Standard 4: water quality

Any proposed SuDS must be based on a thorough water quality risk assessment. The design must use a recognised method, such as the Simple Index Approach or an equivalent, and be tailored to the pollution risks associated with the proposed land use to ensure that runoff is adequately treated.

Standard 5: amenity

SuDS should be designed to be aesthetically pleasing and provide recreational value to the community. They should be integrated into the landscape to create attractive and multi-functional spaces.

Standard 6: biodiversity

SuDS should be designed to support and enhance local wildlife and habitats. This includes contributing to Biodiversity Net Gain (BNG) and Local Nature Recovery Strategies (LNRS).

Standard 7: design of drainage for construction, operation, maintenance, decommissioning and structural integrity

SuDS must be designed with their entire lifecycle in mind. This includes considering long-term operation, maintenance schedules, detailed Construction Method Statements (CMS), and potential failure risks. The design must also ensure the structural integrity of the system against anticipated loading, while also considering durability and biosecurity against invasive species.

These new non-statutory standards mark a turning point for developments in England. SuDS are no longer a simple drainage calculation tacked on at the end of a design; they are a central, defining feature of a project’s success.

For developers, designers, and planners, this means:

• SuDS move from the margins to the master plan. Surface water management must now be considered from day one, influencing site layouts, green space, and road design.
• Collaboration is essential. Engineers and Consultants will need to work more closely than ever with landscape architects and ecologists to create schemes that are not only functional but also beautiful and biodiverse.
• The paper trail is more important. Planning applications will require a new level of detail, with robust evidence justifying your drainage strategy and clear, long-term maintenance plans.
• A fundamental shift from grey to green. The era of relying solely on underground pipes and drainage features is now discouraged as much as is feasible. The future is in creating resilient, visible, and valuable green infrastructure that serves the community and the environment.

The latest updates to the NPPF have put drainage strategies firmly in the spotlight. In response, we’ve seen local authorities issue more holding objections than relying on planning conditions to request extra details like capacity checks or infiltration tests.

While Schedule 3 isn’t in place yet in England. The Welsh Government has introduced new legislation, Schedule 3 of the Flood and Water Management Act 2010, came into force on 7th January 2019. This means that, despite initial concerns, the shift to Schedule 3 in England may not be as daunting as many feared. More information up front will be needed to satisfy the LPA, LLFA and Water Companies before approving a planning application, more specifically, a drainage strategy. 

Adding to this momentum is the new non-statutory guidance. It sets out best practices that closely will likely emulate what Schedule 3 will bring and more, essentially giving us a preview of what’s to come.