Resolving drainage misconnections

It is important that drainage work is carried out by a skilled professional because if it is installed incorrectly, problems can arise with wastewater discharging into the wrong system or local streams.

Identifying drainage systems

Domestic drainage systems come in two main categories – separate systems or combined systems. Separate systems only take foul water (from the toilet, sink and so on) to the sewer, while the rainwater or surface water might go to a stream or river and then into the sea. Combined systems are connected to a main sewer and waste goes to the local treatment plant before it ends up in a river or the sea.

A separate system has two pipes below ground: one for surface water (rainwater) and the other for foul water, which is where the system is replicated in the main sewers. These can easily be identified by two manhole covers, generally side by side, for accessing the pipework.

A combined system does what it says; all water is discharged in one pipe and therefore any line of manholes is singular in many cases. Pipes are laid in straight lines as much as possible, so following manholes can give you a good indication of direction.

Another way of identification might be the age of the property. If a house was built before 1920, it is likely to have a combined system. If it was built after the 1950s, then it will have a separate system. The majority of homes built in the last five to 10 years have a separate system on the property, but actually go to a combined sewer. This is done in readiness for sewer upgrades.

At some older properties, a partially separate system used the rainwater from a garage at the rear to flush the main drain with the surface water. Again, it must not become a foul drain as it could be the wrong size, have no water trap seals or access points.

Discovering misconnections

Drains work using gravity. The point in the road is generally the lowest point while the highest point, also known as the head of the drain, is the furthest shallow point. It will be obvious if alterations have been made over the years and this is often a cause of misconnections. If you suspect a problem, look for building extensions and alterations, new manholes and patched up driveways.

Buildings can often go through changes of use over their lifespan: basements become apartments, garages are converted, homes are extended or land is filled in for additional properties. All these have the potential to result in misconnected drainage that is not visible.

It's common to see a washbasin waste outlet connected into the nearest rainwater pipe or washing machine waste pipe running into a rainwater gulley after a new kitchen has been installed (see Figure 1). Adding a downstairs toilet to the system can lead to a misconnection if it is discharging into a surface water drain simply because it seems to be the nearest.

Digging up that new driveway or path to work on drainage might create shortcuts, taken through a lack of knowledge or failure to take due care and responsibility, making problems for both the customer and anyone subsequently working on the system. These shortcuts can cause issues with contamination if they are not checked properly at the planning stage and, in some cases, a macerator could do the job without the need to excavate.

Where macerator waste from toilets or other fittings is pumped out (to a point), this is done because the drains are either too far away or above the natural gravity gradient. These must go into a foul drain of the appropriate size and not a rainwater pipe/gulley.

Correct route

As we are seeing an increase in flooding in many parts of the UK, discharging rainwater from rooftops and surface water from non-permeable surfaces has increased the volume of water. These must go into surface water drains or suitably designed soakaways into a local stream. Surface water may not always be accepted into a combined drain when alterations are made, as putting greater loads onto existing systems can increase the risk of flooding.

Building control must be consulted before you discharge water to reduce potential flooding or contamination in your area. You certainly don’t want buildings flooded with sewage because of overflowing surface water.

Finding misconnections on a property is done by either using a dye in the water for direction and discharge into the correct locations (with the manholes safely removed) or specialist cameras to help with identification.

This is not a DIY job due to the nature of the work or the potential equipment needed. In many cases drainage work will require inspection and notification to comply with building regulations and to stop incorrect connections occurring, so it's important that installers know what they are doing.

Find out more

ConnectRight is the public face of the National Misconnections Strategy Group. It’s a partnership of organisations that are working to reduce water pollution from drains and sewers. For more information, visit www.connectright.org.uk.

Misconnected drains can pollute local streams, rivers and beaches, damage wildlife and put our health at risk. We will work to reduce the number of misconnected properties in the UK and address other types of pollution from sewers and drains.