Sustainable drainage systems (SuDS): Frequently-asked questions on safety, compliance and design

Designing Sustainable drainage systems (SuDS) that balance function, placemaking and safety is essential as housebuilders face a range of risks from liability and reputation to planning, approval and cost. 

From April 2015 the National Planning Policy Framework made SuDS a requirement for major developments, extended to all developments in December 2024. And as detailed in the June 2026 issue of Housebuilder magazine, further policy developments are expected.

RoSPA has produced more than 3,000 SuDS safety reports for housebuilders since 2009 using its specialist risk rating tool. We give safety guidance based on best practice and experience from the many sites we have reviewed.

Following our recent webinar on designing out SuDS risks, we have compiled answers to some FAQs about managing SuDS safely.

Is a SuDS safety review a legal requirement or just good practice?

While not a legal requirement in itself, a SuDS safety review is widely recognised as a robust and proportionate way of demonstrating that foreseeable risks have been identified, assessed and managed and can help developers, designers and authorities evidence compliance with wider health and safety duties.

Have there been confirmed incidents relating to biological risks linked to SuDS? 

We’ve not come across any such incidents. However, there are confirmed cases of leptospirosis linked to contact with surface waters, drainage systems, ponds, ditches, floodwater and similar environments, which are functionally comparable to SuDS.

Because SuDS can include standing or slow‑moving water and attract wildlife (including rodents), biological hazards such as leptospirosis are recognised as a credible but low‑likelihood risk.

What is your view on placing play equipment in attenuation basins?

We recognise that some designers promote locating play features within attenuation basins or swales as a way of encouraging children’s exposure to “managed risk”. Our position is that any play activity in SuDS features needs to be very carefully justified and tightly controlled. Attenuation basins are, first and foremost, functional drainage assets designed to hold water during storm events, and their condition and behaviour can change rapidly.

From a practical perspective, combining play with flood storage:

• Introduces foreseeable safety risks during and after flood events (e.g. submerged equipment, soft or silty surfaces, debris, hidden trip hazards)
• Creates an operational burden for local authorities, who are then expected to close these areas during flooding, inspect them afterwards, remove silt and debris, and formally determine when they are safe to reopen.

How many occurrences of drowning have been identified in the UK as associated with SuDS? 

While no accidental fatalities have been recorded in the Water Incident Database (WAID) as specifically attributable to SuDS between 2020 and 2024, absence of recorded incidents should not be interpreted as absence of risk. Appropriate risk assessment and management remain necessary.

What are your thoughts on the use of slopes in relation to SuDS?

Current CIRIA C753 guidance accepts side slopes of up to 1:3, and this aligns with RoSPA guidance, which recommends 1:3 or shallower for public-facing SuDS features. In our experience, a well-designed 1:3 grassed slope generally improves the likelihood of self-rescue by an adult or older child under normal conditions.

How can vegetation increase safety? 

Longer grass/vegetation on banks can deter and slow down young children from reaching the water’s edge, as well as catch balls from informal play. We also encourage marginal vegetation at the water’s edge to further deter access. However, vegetation needs to be maintained to allow views over the water to see if anyone is in trouble and to deter any antisocial behaviour. The aim is a controlled balance: vegetation that clearly signals a change in space and discourages access, without obscuring views or making SuDS features feel hidden or unsafe.

What approach can help balance the desire to make SuDS attractive community spaces with the practical adoption requirements from water authorities?

A balanced approach is to engage water authorities early to understand which engineered features are required for adoption and then design around them. Where concrete headwalls, railings or defined structures are necessary, their visual impact can often be reduced by using vegetation to soften barriers and keep amenity spaces separate from operational features.

What are the names of the reports RoSPA recommends from design to handover to a local authority?

RoSPA typically recommends a staged approach to SuDS safety reviews, running from design through to handover and ongoing management. This usually includes a SuDS Desktop Safety Review at the planning or detailed design stage, based on drawings, followed by a SuDS Site Safety Review once features are constructed.

In practice, SuDS reviews can be commissioned at several key points:

• Design stage (desktop review)
• Early construction
• Near completion
• Completion/practical completion, to support handover to a local authority or management body
• Annual or biannual revisits, to review safety as sites mature and usage patterns change.

This approach allows safety issues to be identified early, checked during construction, confirmed at handover, and reviewed over time as the SuDS becomes established. Beyond SuDS safety reviews, RoSPA also offers related services such as Water Safety Reviews, support with Water Safety Management Policies, Leisure SafetyMark accreditation (pools, gyms and saunas), and Public Open Space Safety Reviews.

Are there standard safety recommendations/rules for swales and basins to provide consistency?

There are no single prescriptive “one‑size‑fits‑all” rules for swales and basins, but there is well‑established good practice. As a general benchmark, side slopes of 1:3 or shallower are widely accepted to allow for self‑rescue by an adult or older child.

Barriers or railings are not expected everywhere. They are typically appropriate at headwalls, inlets, outlets or other locations where there is a fall‑from‑height risk. Measures should be site‑specific and proportionate, based on how people are likely to access and use the space.

Similarly, the provision of public rescue equipment should not be automatic wherever there is water. It should be informed by a site‑specific risk assessment, considering factors such as depth, flow, accessibility, visibility and likely users.

At a development or organisational level, consistency is best achieved not through fixed rules, but through a Water Safety Management Policy that sets out clear principles for risk assessment, design responses and decision‑making across sites.

Is there legal guidance for design in school fields or public spaces?

There is no single piece of legislation setting out SuDS design requirements specifically for schools or public open spaces. Instead, safety is governed by general legal duties, such as the Health and Safety at Work etc. Act 1974 and the Occupiers’ Liability Acts and informed by industry guidance like the Construction Industry Research and Information Association (CIRIA) SuDS Manual, Department for Education advice for school grounds, and RoSPA’s Managing Safety at Inland Waters.  In practice, SuDS in these settings should be designed using a site-specific, risk-based approach that is reasonable, proportionate, and defensible.