Connecting to Mains Sewer 

Getting services to a development can be an expensive business. There are two ways in which you can connect to a "public" sewer, either directly or indirectly. Below we explain the differences.

Directly Connecting to Mains Sewer

Sewers managed and or owned by water companies such as Thames Water, are referred to as adopted sewers, they are built to a far more stringent standard, when compared to non adopted sewers.

You cannot connect directly to an adopted sewer without some form of oversight from the Sewer Company, and in some cases you will have to use one of their approved contractors.

A sewer is within you property boundary can be adopted, the easiest way to check this is to order an asset map from you local sewage undertaker. If the sewer on you land is marked as one of there assets then you know it is adopted.

Indirectly Connecting to a Mains Sewer

However, if you were to connect indirectly you could potentially involve the work involved in altering adopted sewers.

By connecting to a private drain or lateral drain you would be subject to building regulations, but could avoid more stringent requirements and expense of connecting direct to adopted sewer.

This is particularly suitable to circumstances where private drains and proposed connection are under the same ownerships, or in some cases where a new development replaces an old one, which uses lateral drain.

The below section was written by a machine.

Technical Guidance: Navigating Mains Sewer Connections

Establishing a connection to a mains sewer is a critical phase in the development of any industrial or residential site. In the UK, the process is governed by stringent regulatory frameworks, primarily the Water Industry Act 1991. Whether you are pursuing a direct connection to an adopted sewer or an indirect connection via a private drain, understanding the hierarchy of drainage and the requirements of local water undertakers is essential for project success. Integrating these infrastructure needs with a site-specific flood risk assessment (FRA) ensures that your drainage strategy is robust and compliant.

Direct Connections and Adopted Sewers

A direct connection involves tapping into a sewer that is managed and maintained by a water company, such as Thames Water or Wessex Water. These "adopted" sewers are built to high engineering standards and require formal approval under Section 106 of the Water Industry Act. Key considerations for direct connections include:

• Asset Mapping: Identifying the exact location and depth of adopted assets is the first step. This prevents accidental damage and informs the engineering design for the connection point.
• Water Company Oversight: Most undertakers require that work on their assets be carried out by approved contractors or under strict supervision to ensure the integrity of the wider network.
• Technical Standards: Connections must be designed to withstand hydraulic loads and prevent blockages, often requiring more complex engineering than private systems.

Indirect Connections and Private Drainage

An indirect connection allows a new development to link into an existing private or lateral drain that eventually discharges into the public network. This route is often more cost-effective as it falls under Building Regulations rather than the more demanding water company adoptions. However, it requires a clear understanding of land ownership and the capacity of the existing private network. If site conditions do not allow for sewer connection, developers must look toward the SuDS hierarchy, beginning with soakaway testing to determine if infiltration is a viable alternative.

Infrastructure and Planning Strategy

Securing sewer connection rights is a fundamental part of the planning statement for any development. Early engagement with water companies and a thorough review of the sustainability strategy can prevent costly delays during the construction phase. With over 15 years of industry experience and a track record of 900+ projects across the UK, SWEL provides the technical authority and professional accreditation (IES/FGS) required to navigate these infrastructure hurdles. Our reports provide the evidence base needed to satisfy building control and secure a project's long-term operational viability.