Septic Tanks Overview

If your house or business is not connected to the mains sewer, your sewage will go to one of the following:

  • septic tank – an underground tank where the solids sink to the bottom and the liquid flows out and soaks through the ground
  • small sewage treatment plant (also known as a package treatment plant) – a part-mechanical system that treats the liquid so it’s clean enough to go into a river or stream
  • cesspool (also called a cesspit) – a sealed tank that collects the sewage
  • a non-standard system, such as a reed bed or trench arch system
General binding rules: small sewage discharge to a surface water

You must read septic tanks and treatment plants: permits and general binding rules before you follow this guidance.

The requirements changed on 1 January 2015. If your system was installed and discharging before 31 December 2014 you have an ‘existing discharge’. If your system was installed and discharging on or after 1 January 2015 you have a ‘new discharge’.

If your discharge causes pollution you may be committing an offence. The Environment Agency will give you advice to help you fix the problem. If your discharge continues to cause pollution the Environment Agency may take enforcement action against you.

Rules for existing and new treatment systems
Use the correct treatment system

You must use a small sewage treatment plant to treat the sewage if you’re discharging to a watercourse such as a river or stream. A sewage treatment plant (also known as a package treatment plant) treats sewage to a higher standard than a septic tank.

Discharges from septic tanks directly to watercourses are not allowed under the general binding rules.

You should get advice from a competent service engineer if you need help understanding what:

  • treatment system you have
  • you are required to do under the general binding rules

British Water provides a list of accredited service engineers. There may be other competent service engineers.

If your septic tank discharges directly to a watercourse, you need to do one of the following as soon as possible:

  • connect to mains sewer
  • install a drainage field (also known as an infiltration system) so the septic tank can discharge to ground instead
  • replace your septic tank with a small sewage treatment plant

You must have plans in place to carry out this work within a reasonable timescale, typically 12 months.

You cannot use a septic tank conversion unit or a reedbed for discharging effluent to a watercourse under the general binding rules. Instead you must either upgrade to a package treatment plant or apply for a permit so that the Environment Agency can assess the risk of using this sort of system in your location. If you apply for a permit you will need to include supporting information to show that the treatment system will treat your sewage to an appropriate standard.

Be advised the above are only extracts from the website. Please visit the links highlighted for a full explanation of grey water run-off.