How to find the closest public sewer to your build site

Finding the nearest public sewer to your site has to be the first step in working out a new build’s drainage layout – but working out where the existing public sewer is isn’t always easy. 

Where is my nearest public sewer and why is this important?

Whether you’re building a single dwelling or a whole estate, you’ll want to connect your drainage system to the existing public sewer as this is the most cost-effective and hassle-free approach for dealing with waste water and sewage from a property. The design of the private sewer system, and also the cost of installing it, will depend on the location of the closest public sewer, so finding out this information is key to knowing how to proceed.

Some public sewers are easily found, as their location is marked on the water authority’s sewer maps, but a high proportion of public sewers aren’t on those maps. Thanks to a change in legislation in October 2011, water authorities became responsible for some sewers that were previously privately owned, and therefore weren’t – and still aren’t – marked on their records. Thames Water, for example, became responsible for an additional 40,000km of sewers!

How to get sewer maps

You can visit your local authority’s offices to inspect their public sewer map, or you can order an asset location search from the water company in question (many of them offer this online through Digdat). This service will give you the location of known water and sewage pipes in the vicinity of your site, including pipe sizes and direction of flow, plus pipe depths and cover levels where this data has been recorded. 

There is a charge for an asset location search to locate your closest public sewer – at the time of writing this varies across the water authorities we work with:

  • Thames Water – £68.72
  • Southern Water – £51.76
  • Anglian Water – £41.83

Existing public sewers that are not on the drainage map

You may find the nearest public sewer is not recorded in detail on the drainage maps held by the water or local authorities. If there are unrecorded public sewers close to where you plan to build, then a site investigation may be needed to determine the actual drainage arrangements (lifting manhole covers, taking levels, possibly CCTV surveys), and it will be necessary to confirm that those sewers have been adopted by the water authority in question.

If there are unmapped sewers close to your development site, and you want to apply for permission to either build near or over them, or to connect to them, then water authorities are likely to ask you to provide as much information as possible in your application. A site investigation is likely to be required. The water company may well ask you to wait before making payment, in case the sewer in question isn’t in fact their responsibility.

If there is no public sewer in the vicinity of the site – which does happen quite a lot in rural areas – then that’s when it might be necessary to consider a sewage treatment plant or a septic tank. It is best to seek specialist advice in these instances to ensure you select the most effective option.

To learn more about how to get sewer maps, or for further information about planning drainage systems for new build developments – including free advice on your project – call us on 01268 950050 or send us an email to [email protected]

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