What is a Lateral drains

Lateral drains are underground pipe sections that carry wastewater from an individual property to the public sewer network. They form a critical part of the drainage infrastructure by linking the private internal drainage system of a building (such as toilets, sinks, and showers) with the larger public system maintained by the local water authority.

Although often overlooked, lateral drains are essential for the safe and hygienic transport of foul and surface water away from properties. They are subject to specific ownership, maintenance, and regulatory requirements, which property owners and developers must understand to ensure compliance and avoid costly repairs or disputes.

What defines a lateral drain

A lateral drain is the part of the drainage pipe that lies outside the boundary of a private property, typically running under public land such as a footpath, verge, or road. It connects the final section of the private drain, which is within the property boundary, to the public sewer. In some cases, the lateral drain may also run beneath neighbouring properties before reaching the main sewer.

Key features of a lateral drain include:

  • It serves a single property (unlike a sewer, which carries flows from multiple properties)

  • It is usually located outside the legal boundary of the property

  • It ultimately connects to the public sewer system

  • It can be shared in rare cases but is still classed as serving one origin point

Before 2011, lateral drains were often considered the responsibility of the property owner. However, legislative changes have since altered the ownership structure across most of the UK.

Ownership and maintenance

In England and Wales, the Water Industry (Schemes for Adoption of Private Sewers) Regulations 2011 transferred responsibility for most lateral drains to local water and sewerage companies. This means that:

  • The water authority is now responsible for maintaining, repairing, and replacing lateral drains that serve a single property but lie outside its boundary

  • Property owners remain responsible for the section of pipe within their boundary up to the point where it meets the lateral drain (known as the private drain)

In Scotland and Northern Ireland, similar rules apply, although specific arrangements may vary slightly depending on local authorities and property types.

This change in responsibility was introduced to simplify ownership, improve network management, and reduce disputes between neighbours and utility providers.

How lateral drains function

Lateral drains are typically gravity-fed, meaning wastewater flows downhill through the pipes due to gravity. They are sized and graded to ensure sufficient flow velocity to prevent sediment build-up while maintaining accessibility for inspection and maintenance.

In residential settings, the typical drainage path is as follows:

  1. Wastewater is generated within the property (e.g. flushing a toilet or using a washing machine)

  2. It flows into the private drain beneath the property or garden

  3. The private drain connects to the lateral drain near the boundary or at a manhole

  4. The lateral drain carries the flow to the public sewer

Some lateral drains may also receive surface water from roofs or paved areas, particularly in combined drainage systems found in older properties.

Materials and construction

Lateral drains can be constructed from various materials, depending on the age of the installation and local standards. Common materials include:

  • Clay pipes (vitrified clay) – commonly used in older systems

  • PVC-u (unplasticised polyvinyl chloride) – the standard material in modern installations

  • Cast iron or pitch fibre – now largely obsolete but still found in some legacy systems

  • Concrete or asbestos cement – sometimes used in larger or industrial-scale laterals

New lateral drains must be designed and installed in accordance with Building Regulations and water authority requirements. Minimum gradients, ventilation, and access for rodding or jetting must be provided to allow for cleaning and maintenance.

Common problems with lateral drains

Like any part of a drainage system, lateral drains are vulnerable to damage, blockage, and degradation over time. Common issues include:

  • Root ingress – tree roots can enter through joints or cracks, leading to blockages and structural damage

  • Pipe displacement – ground movement or poor installation can cause joints to become misaligned

  • Cracking or fracturing – particularly in older clay or pitch fibre pipes

  • Fat and grease build-up – from kitchen waste leading to blockages

  • Misconnections – such as foul water being incorrectly directed into a surface water system

Symptoms of problems in a lateral drain can include slow draining fixtures, foul odours, sewage backing up into the property, or wet patches near the property boundary.

Inspection and repair

When a blockage or fault is suspected in the drainage system, a CCTV drain survey is the most effective way to locate and diagnose issues within lateral drains. These surveys involve inserting a camera into the pipe to assess its condition in real time.

Depending on the nature and severity of the defect, several repair methods may be used:

  • Rodding or jetting to remove simple blockages

  • Root cutting and chemical treatments for root ingress

  • Patch repairs or localised structural repair (LSR) for cracks

  • Full lining or pipe bursting for widespread damage

  • Excavation and replacement as a last resort

Since most lateral drains are now the responsibility of the water authority, repair works on these sections are generally carried out or approved by them, particularly where excavation in public land is required.

Regulations and building control

New lateral drains, especially those installed as part of an extension, new build, or development, must comply with Building Regulations Part H (in England and Wales) and may require approval from the local water company under Section 106 of the Water Industry Act 1991.

Builders and developers are required to:

  • Submit detailed drainage plans for approval

  • Use approved materials and installation techniques

  • Allow for inspection and testing before backfilling

  • Avoid connecting foul drainage to surface water systems and vice versa

Incorrect installation or failure to obtain the necessary approvals can lead to enforcement action, fines, or costly remediation.

Role in property sales and surveys

Lateral drains are an important consideration during property sales, particularly in older homes or areas with known drainage issues. Homebuyer surveys increasingly include drainage checks, and it is common for solicitors to request a drainage search showing whether the property is connected to the public sewer and where the lateral drain runs.

Problems with lateral drains can affect property value, insurance premiums, and planning permissions, especially if defects have not been repaired or ownership is unclear.

Conclusion

Lateral drains are a vital but often hidden component of every property’s drainage system. They ensure that wastewater flows safely from private buildings into the public sewer network, maintaining hygiene and environmental protection.

Understanding how lateral drains work, who is responsible for them, and how they are maintained is essential for homeowners, landlords, builders, and engineers. With proper care, regular inspection, and compliance with regulations, lateral drains can continue to serve their role efficiently for decades, avoiding unnecessary disruption or expense.