Buying a house with a septic tank

January 11, 2021

Why do some houses use septic tanks?

Buying a house with a septic tank comes with its own unique challenges, but that shouldn’t put you off the perfect property.

Most houses are built with mains drainage, which means they are connected to mains sewage and water, operating their sinks, showers, taps, and toilets and handling the wastewater.

Across the UK, 95% of houses are on mains drainage, which leaves 5% of houses operating ‘off mains’. These houses need to have an alternative system to deal with wastewater and drainage, and so that’s where septic tanks come in.

Septic tanks have certain rules and regulations that must be adhered to, so if you are buying an ‘off-mains’ property, you should be aware of what you are taking on.

Regulations for septic tanks

On the 1st of January 2015, the General Binding Rules for small sewage discharges came into law. These rules show you how to manage your system, and if it does not adhere to the General Binding Rules, or you do not have the correct permit, the system will be deemed illegal.

Follow this link to read more about the General Binding Rules.

Buying a house with a septic tank

First things first, you need to get a specific survey done on any property you are looking to buy if it comes with a septic tank. This is the Home Buyers Drainage Survey and is targeted to look for important factors regarding the septic system.

The survey will not only give you an idea of what your off-mains system involves and its condition but will let you know if you currently adhere to the General Binding Rules.

Types of off-mains systems

For off mains properties, there are typically two types of systems you will come across;


This system has a collection tank and no outflow, so they require regular emptying. This is something to consider when looking to buy a property with a cesspit. Will you be able to get regular draining for the cesspit? Is the property easily accessible?

Cesspit costs can run to around £5k per year, and a replacement installation may be around £5k to £6k.

Septic Tanks

Septic tank systems include a tank with a dividing wall that allows effluent to pass between the sections, but retains the solid waste. The liquid waste will then pass into a drainage field, often referred to as a ‘soakaway’ where it is discharged.

From the 1st of January 2020, septic tanks can no longer discharge to Surface Water and so you must check that your drainage field is constructed properly. Refer back to the government General Binding regulations for more information on this process.

The cost of running a Septic Tank can be around £150 per year and a replacement drainage field, if conditions allow, can range from £3k to £6k.

Things to ask the seller

You are entitled to receive the following in writing when looking to buy a property with an off-mains system:

  • A full description of the current system in place
  • Where the system is located on the property
  • Information and records on any maintenance or repairs that have been completed on the system
  • Instructions on how the system should be maintained and when it needs to be checked.

What to consider when buying a property with off mains drainage

If you choose to continue with your purchase, you will need to be aware of the following;

  • You will be responsible for ensuring the septic tank system does not cause pollution in the local environment.
  • You must adhere to the General Binding Rules
  • You won’t pay charges to a water or sewage company but you will have to pay to maintain your system or have it emptied if you have a cesspit.
  • You will need to have your off-mains system checked annually and continue with repairs and maintenance.