Navigating Scotland's Surface Water Connection Policy: A Developer's Guide

For developers planning new projects in Scotland, connecting surface water to the combined sewer network is far from straightforward. Compared with similar sites in England and Wales, the process is considerably more restrictive. Scottish Water’s stringent policies mean careful planning is essential, particularly for greenfield sites. Failing to meet these requirements can result in costly delays, so it is essential to understand the rules early on.

Scottish Water Policy: No New In, What’s In Out

At the core of Scottish Water’s Surface Water Policy is the principle of “no new in, what’s in out”. In simple terms, this means a development must not increase the peak flow or overall volume of surface water discharged to the combined sewer system.

To secure approval, developers need to provide robust evidence, which typically involves:

1. Proving an Existing Connection

You must show that the site already has a surface water connection to the public combined sewer. This is usually confirmed through CCTV surveys or dye testing, and it is best carried out early in the planning stage.

Scottish Water generally accepts either a CCTV survey and/or dye testing to confirm that the site does, in fact, have an existing surface connection to the public combined sewer. This should be considered as early as possible during the planning phase.

It should be noted that it must be demonstrated that a surface water discharge to the combined sewer has existed within five years of the application to Scottish Water.

2. Achieving Zero-Net Volumetric Detriment

This is critical, as Scottish Water define betterment as a decrease in the overall volume of surface water discharging to the Scottish Water network and treatment works, not just peak flow rates.

Developers are expected to reduce surface water volumes by incorporating measures such as:

• Limiting the amount of new hardstanding where possible
• Introducing rainwater harvesting for non-potable use
• Using infiltration techniques such as soakaways or permeable paving, supported by BRE 365 infiltration testing carried out at an early stage

3. Exhausting All Other Alternatives

Before an application will be approved, you must demonstrate that all other disposal methods have been fully explored. These include reuse, infiltration, discharge to a watercourse, or connection to a surface water sewer.

Scottish Water sets clear guidance based on Housing Unit Equivalent (HUE) and the proximity of a potential receptor:

• For developments of 10 HUE or fewer, connection to a watercourse or sewer is required if one exists within 50 metres (unless proven impractical due to service clashes or obstructions, supported by drawings).
• For developments of more than 50 HUE, there is no set distance limit.

If pumping would be required to reach a receptor, this can be used as justification that a direct connection is not feasible. In these cases, supporting evidence will usually need to include:

• A topographical survey
• A site investigation
• Section drawings

Why Early Planning Matters for Developers in Scotland

Scotland’s surface water policies place significant responsibility on developers to provide clear evidence and consider all drainage options before approaching Scottish Water. The process can be complex, but early action makes a big difference.

At Aegaea, we have delivered Surface Water Drainage Strategies for projects across Scotland, from small rural developments to large-scale urban schemes. With the right expertise, you can find a solution that balances regulatory requirements with the practical needs of your site.