What Is a Shared Septic Tank?

A shared septic tank is an off-mains drainage system that receives wastewater from more than one property.

This type of arrangement can be found around rural properties, converted farm buildings, groups of cottages and developments where connecting every individual property to the public sewer is not practical.

The properties may share a septic tank, sewage treatment plant, drainage field, pipework or a combination of these.

One important distinction is that the physical system and the legal arrangements surrounding it are not necessarily the same thing. The tank may, for example, be situated entirely within one property’s land while serving several neighbouring homes.

Who Is Legally Responsible for a Shared Septic Tank?

The Environment Agency defines the person responsible for a septic tank or sewage treatment plant as its operator.

Government guidance specifically says that if your property shares the system with other properties, you are jointly responsible for it.

This means that responsibility for complying with the General Binding Rules does not necessarily belong solely to the person whose garden contains the tank.

Where several properties use the same system, more than one property owner may therefore have responsibilities relating to its operation, maintenance and discharge.

Does Joint Responsibility Mean Everyone Pays an Equal Share?

Not necessarily.

The General Binding Rules establish environmental responsibilities for operators, but they do not determine how neighbours must divide every maintenance, emptying, servicing or repair bill between themselves.

The financial arrangements may instead be set out in:

• Property title documents
• Deeds
• Easements
• Maintenance agreements
• Historic agreements between property owners
• Other contractual arrangements

If you are buying a property connected to a shared system, your solicitor or conveyancer should establish what rights and obligations attach to the property.

A drainage survey can assess the physical system, but it does not replace legal advice about ownership or the division of costs.

What Should I Check Before Buying a House With a Shared Septic Tank?

A shared private drainage arrangement deserves particular attention during a property purchase because you are potentially taking on responsibility for infrastructure that you do not control entirely yourself.

Before exchange, it is sensible to establish:

• What type of drainage system serves the property
• How many properties use it
• Where the tank or treatment plant is located
• Where the system discharges
• Where the drainage field is located, if there is one
• Who currently arranges emptying and maintenance
• How the associated costs are divided
• Whether maintenance and servicing records are available
• Who has rights of access to the system
• Whether the system appears to comply with the General Binding Rules

A specialist septic tank homebuyer survey can help establish the physical condition and configuration of the drainage system before you become responsible for it.

What Do the General Binding Rules Require?

The General Binding Rules apply to small sewage discharges from septic tanks and sewage treatment plants in England.

Among other requirements, the system must be operated and maintained correctly, must not cause pollution and must use an appropriate method of treatment and discharge.

The system must also be properly maintained by someone who is competent, and waste sludge must be disposed of by an authorised person.

The precise requirements depend partly on whether the discharge goes to the ground or to surface water and whether it is classed as a new or existing discharge.

If the applicable General Binding Rules cannot be met, an environmental permit or changes to the drainage arrangement may be required.

Can a Shared Septic Tank Discharge Into a Ditch or Stream?

A septic tank itself must not discharge directly into surface water such as a stream, river or watercourse.

Septic tank effluent normally needs to discharge to the ground through an appropriate drainage field.

A suitable sewage treatment plant can, in some circumstances, discharge treated effluent to surface water, provided the relevant General Binding Rules and site requirements are met.

This is particularly important when buying an older rural property. A shared system may have been installed many years ago, and simply because it has operated in the same way for a long time does not necessarily mean its current discharge arrangement is satisfactory.

Boxall Ward can carry out an off-mains drainage compliance check where there is uncertainty about the system or its discharge.

What Happens When One of the Properties Is Sold?

The General Binding Rules require the existing operator to give the new operator written information about the sewage treatment and drainage system when a property is sold.

This should include information such as:

• A description of the treatment and drainage system
• The location of the main parts of the system
• The location of the discharge point
• Details of alterations to the system
• Maintenance requirements
• The manufacturer’s maintenance manual, where available
• Maintenance records, where available

With a shared system, it is also sensible for the buyer’s solicitor to establish exactly what legal rights and responsibilities accompany the property.

The fact that another homeowner has historically organised the maintenance should not simply be taken as proof that the new owner has no responsibility.

What If the Septic Tank Is on My Neighbour’s Land?

A septic tank being physically situated on another property’s land does not necessarily remove your responsibilities if your property uses the system.

You should establish what rights exist for access, maintenance, emptying, repair and replacement.

For example, a tanker may need access to empty the tank, contractors may need access for servicing and substantially greater access could be required if the system eventually needs to be replaced.

These rights are particularly important during a property purchase and should be checked through the conveyancing process.

What If One Owner Refuses to Maintain the Shared System?

A shared system works best when everyone understands how it is maintained and who is responsible for arranging the necessary work.

If maintenance is neglected, the consequences can affect every property using the system. Problems may include blockages, sewage backing up, treatment plant failures, drainage field damage or pollution.

Where there is disagreement about contractual obligations or payment responsibilities, property owners may need legal advice about the agreements or rights applying to their particular properties.

The environmental requirements applying to the drainage system are a separate issue: operators still need to ensure that the system complies with the applicable rules.

Should a Shared Septic Tank Be Surveyed Before Buying?

There are strong reasons to have a shared off-mains drainage system inspected before purchasing a property connected to it.

You are not simply assessing an underground tank. You need to understand a system that may involve several properties, shared pipework, a drainage field and legal access arrangements.

A specialist inspection may help establish:

• What type of system is installed
• Its apparent condition
• The visible inlet and outlet arrangements
• How the property connects to the shared system
• Where the wastewater ultimately discharges
• Whether there are signs of failure or poor performance
• Whether further investigation or remedial work may be required
• Whether there appear to be General Binding Rules concerns

For more information, see what a septic tank compliance inspection actually checks.

Can One Property Owner Take Responsibility for the Whole System?

There may be practical arrangements where one owner organises servicing, emptying or maintenance on behalf of everyone using the system.

That can make managing a shared drainage system considerably easier.

However, an informal arrangement where one neighbour happens to make the telephone calls should not automatically be assumed to change the underlying legal or environmental responsibilities attached to the properties.

If ownership or responsibility is unclear, the relevant property documents should be checked.

What Are the Warning Signs of Problems With a Shared System?

Possible signs that a shared septic tank or treatment system needs attention include:

• Slow or backing-up drains
• Persistent sewage smells
• Wet or boggy ground around the drainage field
• Sewage appearing at ground level
• Repeated blockages
• Treatment plant alarms
• Pump or mechanical failures
• Disagreements about unexpectedly frequent emptying

Because several properties may be feeding into the same system, diagnosing the source of a problem can be more complicated than with an individual installation.

Early investigation can help prevent a relatively manageable fault from turning into a much larger repair.

The Bottom Line

If your property shares a septic tank or sewage treatment plant with other properties, you will normally be jointly responsible for the system under the General Binding Rules.

That does not necessarily tell you how repair and maintenance bills should be divided. Those arrangements may depend on deeds, property titles or agreements between the owners.

If you are purchasing a property with shared private drainage, there are therefore two separate things to establish: what condition the drainage system is in, and what legal responsibilities come with the property.

Boxall Ward can inspect shared septic tanks and sewage treatment systems, assess their condition and discharge arrangements, and advise on potential off-mains drainage compliance issues.

Call 01903 815377 or contact Boxall Ward to discuss a private drainage survey or compliance inspection.

Frequently Asked Questions