Non-mains drainage
Non-mains drainage is used when mains sewerage is not available. It’s effective if correctly managed and maintained. The three main systems are:
- package treatment plants
- septic tanks
- cesspools
A package treatment plant can treat sewage to the highest standard and is the only type of treatment that’s allowed to discharge straight into a river (subject to consent from the Environment Agency). There are several different types of package sewage treatment plants available, each with a slightly different treatment technique. Each type provides a treatment unit or biological zone where the sewage comes into contact with microorganisms that break down the organic matter in the sewage.
A septic tank is where sewage is stored in a watertight tank in which bacteria break down solid matter to one third of its original volume. Settled solids are retained and a clear liquid flows out to a land drainage soakaway system. The land must be tested to ensure there is a large enough area available to take this drainage.
A cesspool is a watertight underground tank. Older cesspools are lined with brick or concrete, and more modern ones with plastics, polythene or steel. Foul water is stored until the time of disposal. A cesspool must be pumped out or otherwise emptied by a competent contractor. It’s an offence for anyone other than a competent contractor to do this.
Find out more about septic tanks and sewage treatment plants on GOV.UK
If your cesspool or septic tank overflows or leaks
You’re responsible for getting it repaired. Under the Public Health Act 1936, it’s an offence to allow a cesspool or septic tank to overflow or leak. This carries a fine of up to £200 and a further £2 per day that the offence continues.
If a cesspool or septic tank overflows or leaks polluting a water course, the Environment Agency can prosecute under the Water Resources Act 1991. A conviction carries a fine of up to £20,000, and/or up to three months' imprisonment.