What is a Lateral

A lateral is a private drain or sewer pipe that transports wastewater from a property to a public sewer. It serves as the final section of a property’s drainage system before the waste enters the public infrastructure owned and maintained by a local water authority. Laterals can be found in both residential and commercial drainage systems and are essential for the safe and legal disposal of foul water and, in some cases, surface water.

Although small in scale compared to public sewers, laterals perform a critical role in the overall wastewater management process. They form the interface between privately maintained plumbing systems within a building and the publicly operated networks that carry waste to treatment facilities.

What defines a lateral

A lateral drain or sewer typically begins at the property boundary or shortly before it, depending on the layout, and runs underground to the public sewer. It differs from internal private drains, which carry waste within the property, and from the public sewer system, which serves multiple buildings and is maintained by a statutory undertaker.

Key characteristics of a lateral include:

  • It carries waste from a single property or group of connected private drains

  • It usually runs under third-party land, such as footpaths, driveways, or shared access ways

  • It ends at the point of connection with the public sewer, typically at a manhole or direct junction

  • It may be the legal responsibility of the water company, depending on local legislation

Laterals are essential for ensuring that each property has a direct and uninterrupted route for waste discharge.

Relationship to private drains and public sewers

The drainage system of any property consists of three major parts:

  1. Private drains – These are the pipes within the boundary of a property that carry waste from appliances and fixtures (e.g. toilets, showers, washing machines) to the edge of the property.

  2. Lateral – This is the section outside the boundary, continuing the flow from the private drains to the public sewer.

  3. Public sewer – A network of large pipes that transports waste from multiple properties to treatment plants.

Understanding the distinction is important because it defines who is responsible for maintaining and repairing each section.

Ownership and responsibility

In the United Kingdom, a major shift in drainage responsibility occurred in October 2011 with the implementation of the Private Sewer Transfer Regulations. These changes transferred ownership of most lateral drains from private individuals to local water and sewerage companies.

As a result:

  • The section of drain within the property remains the owner’s responsibility

  • The lateral drain, once it crosses the property boundary, becomes the responsibility of the water authority

  • Repairs and maintenance of the lateral are handled by the authority, including any work beneath public highways or neighbouring land

There are some exceptions to this rule, such as privately managed pumping stations or lateral sewers not yet adopted by the water company, but in general, the system is designed to reduce confusion and ensure consistent management.

Construction and materials

Lateral pipes may be constructed from a variety of materials, depending on the age of the installation and prevailing construction standards at the time. Common materials include:

  • Vitrified clay – Durable and common in older systems

  • uPVC – Lightweight and widely used in modern systems

  • Cast iron or ductile iron – Found in some commercial or historical installations

  • Concrete or asbestos cement – Less common today due to performance and health considerations

Laterals must be installed at the correct gradient to ensure efficient flow and avoid blockages. Access chambers or rodding points are often required for inspection and maintenance, especially where the lateral exceeds a certain length or passes under obstructions.

Common problems affecting laterals

Because laterals are buried and often out of sight, problems can go unnoticed until more serious symptoms arise. Common issues include:

  • Tree root intrusion – Roots can penetrate joints or cracks, causing blockages and structural damage

  • Ground movement – Soil settlement or subsidence can lead to pipe misalignment or collapse

  • Cracks and fractures – Ageing materials can deteriorate over time, leading to leaks and infiltration

  • Grease build-up and blockages – Improper waste disposal can restrict flow

  • Vermin ingress – Rats and other pests can enter through damaged laterals

Symptoms of a failing lateral may include slow draining fixtures, unpleasant odours, sewage backups, or wet patches near the property boundary.

Inspection and repair techniques

When a lateral is suspected to be damaged or blocked, CCTV drain surveys are typically used to diagnose the issue. These allow engineers to visually inspect the interior of the pipe without excavation.

Repair methods depend on the extent and type of damage:

  • Rodding or jetting – To clear blockages and restore flow

  • Localised patch lining – To seal cracks or leaks in a specific area

  • Full lining – A resin liner is inserted along the entire length to restore structural integrity

  • Excavation and replacement – Used when the pipe is beyond repair or collapsed

  • Pipe bursting – A trenchless technique where a new pipe is pulled through the old one

Where the lateral is the responsibility of the water company, these works will be carried out or approved by them, especially if located under public land.

Building regulations and development

New properties or extensions must have properly designed drainage systems that include compliant lateral connections. Under Part H of the Building Regulations in England and Wales, developers must:

  • Use appropriate materials and methods

  • Ensure proper gradients and access for cleaning

  • Apply for permission to connect to the public sewer (Section 106 of the Water Industry Act 1991)

  • Avoid surface water discharge into foul sewers unless permitted

Incorrect installation or unauthorised connections can result in penalties and forced remedial work.

Role in sustainable drainage and modern design

In new developments, laterals are often integrated with sustainable drainage systems (SuDS) to reduce runoff and prevent overloading of the public sewer. While SuDS elements manage stormwater at the surface, laterals continue to play a role in directing treated or attenuated flows to suitable discharge points.

In some cases, surface water is directed to soakaways, swales, or watercourses, meaning a lateral may only carry foul water. These separation strategies are increasingly encouraged to improve water quality and reduce the burden on wastewater treatment facilities.

Conclusion

A lateral is a small but essential part of a property’s drainage system. It connects private waste flows to the public sewer and ensures the safe, efficient, and regulated removal of wastewater from buildings. With changing legislation, clearer ownership responsibilities, and modern repair techniques, laterals are easier to manage than in the past.

Understanding the function and maintenance needs of laterals helps property owners, developers, and engineers ensure compliance, prevent damage, and maintain reliable drainage performance. As part of the broader effort to improve urban infrastructure, the proper installation and care of lateral drains remain a key priority in sustainable and resilient water management.