What is a Private sewer

A private sewer is a section of underground drainage infrastructure that collects and conveys wastewater from multiple properties or buildings but is not part of the public sewer system. Unlike public sewers, which are owned and maintained by a local water authority or utility company, private sewers are typically owned jointly by the property owners whose buildings are connected to the network. This collective ownership also means shared responsibility for maintenance, repairs, and compliance with regulations.

Private sewers often exist within housing developments, commercial estates or older urban areas where shared drainage systems were installed before legislation defined sewer adoption and transfer processes.

Defining a private sewer

The term “private sewer” applies when the following conditions are met:

  • It serves more than one property

  • It lies outside the curtilage (boundary) of those properties

  • It has not been adopted by the public sewerage authority

  • It carries foul water, surface water or both

It is important to distinguish between:

  • Private drains, which serve a single property before connecting to a sewer

  • Private sewers, which serve multiple properties and lie beyond the property boundary

  • Public sewers, maintained by the water company under statutory obligations

Until relatively recently, many shared sewers remained private even though they served entire streets or developments. Changes in UK legislation have addressed this legacy.

Ownership and maintenance responsibility

Where a sewer is private, the responsibility for its upkeep lies with the property owners it serves. This includes:

  • Ensuring the sewer is not blocked or damaged

  • Paying for repairs or replacement works

  • Accessing and coordinating shared maintenance with other owners

  • Avoiding misuse or introduction of harmful substances

If a problem arises in a private sewer, affected property owners must work together to arrange inspection, clearance, or remedial work. This can lead to disputes or confusion when responsibility is unclear.

In the case of a multi-unit building (such as a block of flats), responsibility typically falls to the freeholder, management company or residents’ association.

The 2011 sewer transfer in England and Wales

To address the issues associated with thousands of kilometres of private sewers, the UK government introduced legislative reform under the Water Industry (Schemes for Adoption of Private Sewers) Regulations 2011. From October 2011, most private sewers and lateral drains connected to the public sewer network were transferred to the ownership of the local water company.

This transfer applied to:

  • Private sewers serving multiple properties

  • Lateral drains running outside the property boundary but serving only one building

The aim was to relieve homeowners of the cost and complexity of maintaining shared underground infrastructure. However, certain exclusions remain.

When a private sewer still exists

Not all sewers were transferred in 2011. A private sewer may still exist if:

  • It serves buildings constructed after 1 July 2011 and was not adopted by the water company

  • It has never connected to a public sewer (e.g. it discharges to a private sewage treatment system)

  • It was built without complying with Building Regulations or adoption agreements

  • It serves a commercial or industrial estate where adoption was not pursued

In such cases, the property owners retain full responsibility for its condition and functionality.

Legal and environmental responsibilities

Owners of private sewers must comply with a number of obligations, including:

  • Maintaining the structural condition of the sewer to avoid pollution or flooding

  • Avoiding the disposal of fats, oils, chemicals or non-degradable materials into the system

  • Ensuring that access is available for maintenance and emergency work

  • Preventing tree root ingress and groundwater infiltration

Pollution incidents or illegal discharges from a private sewer can result in fines or enforcement action by the Environment Agency or local authority.

Typical problems in private sewers

Common issues affecting private sewers include:

  • Blockages caused by inappropriate waste, fat build-up or root intrusion

  • Structural damage due to ground movement or ageing materials

  • Collapsed pipework, particularly in older clay or pitch fibre sewers

  • Disputes between neighbours over repair responsibility or cost sharing

  • Difficulty accessing buried infrastructure located across private land

Such problems can lead to sewage backing up into homes, unpleasant odours or contamination of nearby land or watercourses.

Maintenance strategies

Property owners sharing a private sewer can adopt several good practices to ensure reliable operation:

  • Commissioning regular CCTV drain surveys to detect early issues

  • Agreeing to a shared maintenance plan or legal covenant

  • Keeping records of system layout, repairs and ownership responsibilities

  • Using qualified drainage professionals for inspections and repairs

  • Educating residents or occupants about proper waste disposal

Proactive cooperation can prevent emergencies and reduce overall maintenance costs.

Connection to a public sewer

In some cases, the owners of a private sewer may seek to connect their system to the public sewer network. This typically involves:

  • Applying to the local water company for approval

  • Meeting design and construction standards for new pipework

  • Agreeing to adoption or maintaining the new section privately

In developments or conversions, a Section 104 agreement under the Water Industry Act 1991 may be used to formalise the adoption of newly constructed sewers.

Conclusion

A private sewer is a shared drainage system not maintained by the local water authority, typically serving more than one property and located outside individual property boundaries. While many were transferred to public ownership in 2011, numerous private sewers still exist and require ongoing maintenance by the affected owners.

Understanding ownership, responsibilities and maintenance requirements is essential for avoiding legal issues, system failure and environmental damage. As urban areas grow and drainage regulations evolve, private sewers will continue to play a role in managing wastewater, particularly in older developments and rural communities.