What is a Cesspool

A cesspool, also known as a cesspit, is a sealed, watertight underground tank designed to collect and temporarily store all wastewater and sewage from a property. Unlike septic tanks or sewage treatment plants, a cesspool does not treat or discharge its contents. Once full, the cesspool must be emptied by a licensed waste carrier using a vacuum tanker. Because it has no outlet, a cesspool is essentially a holding facility, and as such, it represents the most basic—and typically the most expensive to maintain—form of off-mains sewage management.

Cesspools are used in situations where no mains drainage is available and where the discharge of effluent into the ground or watercourses is either not possible or not permitted due to environmental constraints. Their use in the UK is now relatively limited and generally discouraged for new developments, except in very specific circumstances.

For property owners, drainage engineers, and environmental professionals, it is essential to understand the functionality, regulatory requirements, maintenance needs, and alternatives to cesspools when dealing with rural properties or sites with restricted drainage options.

Function and Design

A cesspool functions purely as a storage unit for all liquid waste, including:

  • Blackwater (from toilets) 
  • Greywater (from sinks, baths, showers, dishwashers, and washing machines) 
  • Rainwater and surface drainage (if connected) 

Once installed, the cesspool continuously fills with incoming waste. It does not treat, filter, or discharge any of the contents. Once it reaches a pre-determined capacity, it must be emptied to prevent overflow and environmental contamination.

Typical Features of a Cesspool

  • Sealed construction: The tank must be completely watertight to prevent leakage or groundwater ingress. Modern units are often constructed from reinforced concrete, GRP (glass-reinforced plastic), or polyethylene. 
  • Access hatch: A secure manhole or inspection cover provides access for emptying and inspection. 
  • Ventilation: A vent pipe allows gases to escape safely, reducing internal pressure and minimising odours. 
  • Level indicator: Many cesspools include an alarm or visual indicator to alert the user when the tank approaches capacity. 

Cesspools are available in a range of sizes, typically from 10,000 to 45,000 litres (10–45 m³), depending on property size and expected usage. In high-use or commercial applications, larger or multiple tanks may be installed.

Typical Use Cases

Although their popularity has declined, cesspools are still used in specific scenarios, including:

  • Remote or rural properties without access to mains sewerage. 
  • Sites with unsuitable ground conditions (e.g. clay soils or high water tables) that prevent the use of soakaways or drainage fields. 
  • Environmentally sensitive areas such as Source Protection Zones (SPZs), where discharges could threaten groundwater quality. 
  • Temporary or seasonal facilities like construction site offices, campsites, or event venues. 
  • Heritage or protected sites, where excavation for drainage infrastructure is restricted. 

It is important to note that new installations of cesspools are subject to strict planning and regulatory scrutiny, and alternative solutions are usually preferred wherever feasible.

Regulatory Requirements in the UK

Cesspools are subject to a range of legal and environmental controls in the United Kingdom. Their installation and operation must comply with several key pieces of legislation:

Building Regulations

  • Part H of the Building Regulations 2010 sets out minimum requirements for the siting, design, and capacity of cesspools. 
  • A cesspool must have a minimum capacity of 18,000 litres for a two-person household, with an additional 6,800 litres per person thereafter. 

Environmental Permitting

  • Unlike septic tanks and sewage treatment plants, cesspools do not benefit from the General Binding Rules and always require regular emptying by a registered waste carrier. 
  • Because there is no discharge, a permit from the Environment Agency is typically not required, but local planning authorities may impose conditions on their use. 

Planning Permission

  • Installation of a new cesspool almost always requires planning permission. 
  • Approval will depend on site constraints, availability of alternative options, and proximity to sensitive water receptors. 

Waste Disposal

  • Emptying must be carried out by a licensed waste disposal company and the contents transported to an authorised treatment facility. 
  • Records of waste transfer, including the Waste Transfer Note, must be kept as evidence of legal compliance. 

Installation Considerations

Proper installation of a cesspool is essential for long-term performance and legal compliance. Key considerations include:

Siting

  • Must be located at a safe distance from buildings, boundaries, and water sources. 
  • Should be positioned for easy access by emptying vehicles, ideally within 30 metres of a roadway. 
  • Avoid placing tanks in areas prone to flooding or surface water accumulation. 

Ground Conditions

  • Ground bearing capacity must be assessed to ensure structural stability. 
  • In high water table areas, anti-floatation measures (such as concrete anchors) may be necessary. 

Access and Maintenance

  • Access covers must be secure yet accessible for inspection and emptying. 
  • Level alarms should be installed and tested regularly. 

Professional installation by an experienced contractor is strongly recommended to ensure compliance with regulations and avoid costly failures.

Maintenance and Operation

Unlike treatment systems that require servicing, a cesspool’s primary maintenance requirement is regular emptying. The frequency of emptying depends on the tank size and the volume of wastewater generated.

For example:

  • A 2-person household using a 18,000-litre tank may need emptying every 6–8 weeks. 
  • Larger families or properties with higher water usage may require more frequent service. 

Maintenance tips include:

  1. Monitor usage carefully and set up reminders or automated alarms. 
  2. Avoid non-degradable items entering the system (e.g. wet wipes, nappies, sanitary products). 
  3. Use water efficiently to minimise fill rates. 
  4. Maintain access for tanker vehicles, especially in rural or poorly surfaced areas. 
  5. Schedule emptying in advance, especially in holiday periods or remote locations where service availability may be limited. 

Neglecting maintenance can lead to unpleasant odours, overflow, legal breaches, and environmental damage.

Environmental Impacts

Because cesspools do not treat waste, they pose a greater risk to the environment if poorly maintained or improperly constructed. Potential issues include:

  • Leakage into groundwater or surrounding soil, contaminating drinking water sources. 
  • Overflow during periods of high rainfall or delayed emptying. 
  • Emission of odorous gases if not properly vented. 
  • Carbon footprint associated with frequent tanker visits and waste transport. 

For these reasons, modern environmental policy and planning practice generally discourages cesspool use unless no alternatives are viable.

Alternatives to Cesspools

Wherever possible, more sustainable and cost-effective options should be considered. These include:

1. Septic Tanks

  • Basic onsite treatment system that separates solids and discharges liquid effluent to a drainage field. 
  • Lower operational cost but only suitable where ground conditions permit infiltration. 

2. Sewage Treatment Plants

  • Compact units that treat sewage to a high standard, allowing discharge to watercourses (with appropriate consent) or drainage fields. 
  • More expensive to install but lower long-term maintenance and environmental impact. 

3. Pumped Mains Connection

  • Where gravity connection is not feasible, a pumped system may allow access to the public sewer network. 
  • Requires capital investment but offers long-term reliability and regulatory compliance. 

The choice of system should be guided by a drainage survey, percolation testing, and consultation with regulatory authorities.

Conclusion

A cesspool is a sealed underground tank used to store sewage and wastewater from a property in the absence of a mains drainage connection or viable discharge option. While simple in concept, cesspools demand careful management and regular emptying to remain compliant and safe. Their use is increasingly rare and generally reserved for circumstances where no other drainage solution is practicable.

For homeowners, developers, and drainage professionals, understanding the implications, responsibilities, and alternatives associated with cesspools is essential to ensure environmentally sound and legally compliant wastewater management. As sustainability and water protection become more critical in planning and policy, the role of cesspools is expected to remain highly limited, with greater emphasis placed on advanced treatment technologies and integrated drainage strategies.