What is drain mapping?

Drain mapping is the method by which the layout of drains is established to create a map of the drainage system in a given area or around a certain property.

Why might drain mapping be necessary?

It’s very important when planning further building in an area. For example, when building an extension to a property the layout and scope of existing drains needs to be established if it isn’t known already. Once this information is gathered, then decisions can be made as to whether the drainage system needs an alteration or an upgrade and where and how to connect the new build to the existing system.

Drain mapping is a key part of a drains survey, such as those ordered by house buyers considering the purchase of a property. In some cases their surveyor may insist on one.

Major problems to the drains can be very expensive to repair so a knowledge of their condition and layout can be vital. This might be of particular importance in older properties where records of drain positioning might be inaccurate or may not even exist.

Drain mapping may also be required when there are problems with the drains such as a major blockage, inefficient operation or leaks. Knowing accurately how the drains are laid out makes fault finding and repair work more effective. This is especially valuable in the case of recurring problems – a more deep seated problem can be revealed once an accurate map of the drains layout is established.

Methods of drain mapping

The techniques used vary in their complexity:

Water flow tracing – Flushing

The most straightforward method is when the flow of water is checked at various stages of its route through and out of a property. The test is run by simply running a tap or pouring buckets of water down the drain and checking where the water flows by, say, lifting a manhole cover nearby and seeing if the water from the running tap flows through.

Flushing a toilet and maybe adding a piece of tissue paper and then seeing where it appears elsewhere in the drainage route is sometimes used. Again, lifting a manhole cover and watching the water flow and looking out for the tissue paper will give a general idea of how the drains are routed.

Water tests

This is the analysis of the type of water passing through the drainage system. Tests can reveal whether the water contains elements of sewage, waste or whether it is ‘clear’ water. This can indicate where the water flowing through a given drain has come from and helps to assess routes.

Dye testing

Similar to ‘water flow tracing’ above, but a more comprehensive procedure as different water flows can be analysed by using different coloured dyes to colour the water thus making it easy to follow its flow.

The dye is added via a sink, the toilet or directly into a drain. The dye itself comes in tablet or powder form, is totally environmentally friendly and won’t mark or stain bathroom suites and kitchen sinks.


CCTV is the most involved and comprehensive drain mapping procedure, a special camera is lowered into the drains and moves along recording video footage and still pictures.

Thanks to the latest technology, there’s no need to dig a hole to make room for the camera – it can be lowered easily via a manhole cover. The camera technology also makes for very high quality footage, so along with drain mapping, detailed pictures of faults in the drainage system can be recorded.

A permanent record

An accurate physical map of the drains is created and supplied, and footage and stills from a CCTV survey is supplied to provide a comprehensive record of the drains layout.

Our drain mapping services will provide you with an accurate map of all drains leading out from a property. Get in touch with London Drainage Facilities today to learn more.

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