Drain Mapping on your property is a legal requirement

Published 6th December 2022

What is drain mapping?

Drain mapping, sometimes known as asset mapping, is the process of checking out the layout of drains and sewers beneath your property or area of land for which you are responsible as an owner or tenant. The map or plan should include the location of existing foul water networks, manholes and gullies. It is a legal requirement that all premises have a drainage plan.

Do you have a drain plan?

If not, you should as a matter of urgency start the process. Drainage systems can very quickly transport pollutants off site and into the environment. It is therefore important to make a plan of your drains to help you use them correctly, enable you to carry out maintenance and deal more effectively with pollution if there’s a spill, leak or other incident.

Have you taken over a site or premises and can’t locate a drain map? Perhaps you suspect that your current drain map is out of date? You can start at your local authority’s offices to inspect their public sewer map, and you can order an asset location search from the water company in question.

If you prefer there are specialist consultancy firms who will take care of the whole process for you.

In particular, older properties may have an inaccurate drainage plan and carrying out drainage

mapping will help site managers and engineers make informed decisions about whether it needs an alteration or upgrade.

Do you know where do your drains go?

This might seem like a simple question that an accurate drain map can answer, showing where surface water drains are located and where they discharge to any nearby ditches, streams, rivers, storm drains or other watercourses.

It will also show where drains that connect to the sewer are located. These can be sewers that remove dirty water only, or combined sewers, which take dirty water and runoff from some surface water drains to the sewage treatment plant.

This information should be available when you need it:

  • For activities planned on your site
  • For the inspection and maintenance of your drains
  • For when contractors or third parties need this information.

What you need to include in your drain plan

  • Location of the drains
  • Type of drains – surface water, foul water, or combined
  • Direction of flow
  • Where drains leave your property
  • Where they discharge into. For example, a watercourse, clean-water soakaway or sewage treatment works

The plan should be shared so that all personnel working on site can understand it and easily find it when required.

Produce a clear plan of your site, with all the drains identified, and include the direction of the drain, where it leaves your premises and where it goes.

Include any nearby watercourses in your plan. Colour code manhole covers and drains, red for the sewer and blue for surface water. This can prevent accidental contamination of the surface water drain.

Do you need more information?

Legislation varies within the UK. We recommend you consult for further information:

More information on this topic is available on the UK Gov website:

Scotland, Wales and NI
Guidance for Pollution Prevention Understanding your environmental responsibilities June 2021