Private sewage treatment in an area with a public sewer

The use of private domestic sewage treatment in a sewered area is only permissible if connection to the public sewer is not feasible.

Generally, if the boundary of a single property is within 30 metres of a public sewer, it is considered feasible to connect. For larger developments, the number of properties is multiplied by 30 to calculate the distance at which it is still feasible to connect.

Domestic sewage is defined as sewage arising from normal domestic activities, including schools, restaurants, hotels, holiday parks and nursing homes.

If a water company refuses to allow you to connect to the public sewer

You have the right to connect to a public sewer. If a water company refuses to adopt your connection, you must appeal the decision with Ofwat before you can apply for a permit for a private sewage treatment system.

A lack of capacity in the sewer is not a valid reason for a water company to refuse a connection.

We will refuse to issue a permit if you have not appealed the sewerage undertaker’s (usually the water company) decision to Ofwat. You must carry out the following steps before we will consider a permit application:

  1. Approach the sewerage undertaker to reach an agreement for a connection to the foul sewer
  2. If the sewerage undertaker refuses connection to the public sewer, request that they adopt the proposed treatment system
  3. If the sewerage undertaker refuses both of the above, you must appeal the refusal with Ofwat

If a sewerage undertaker agrees to adopt your system, we may grant a permit subject to our environmental assessment.

When it might not be feasible to connect to a public sewer

If you are within the distance considered feasible to connect to a public sewer but are still considering a private sewage treatment plant, you must provide evidence of why it is not feasible to connect to the public sewer.

You need to tell us if:

  • the cost of connecting to the public sewer is greater than the cost of installing a private treatment system
  • there are any practical difficulties in connecting to the public sewer, for example if you need to cross a watercourse or land owned by someone else
  • there are environmental benefits to installing a private sewage system
  • you are providing a funded management and maintenance scheme

There is no obligation for the developer to contribute to costs of connection incurred off-site.

You can read more about a water company’s legal obligations on Ofwat’s website.

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