Foul Water

Foul water drainage is installed underground and is required to carry waste-water from appliances in bathrooms, kitchens or utility rooms away from the building. For properties connected to the mains drainage, the foul water drainage system will connect to the main sewer which will then transport the waste water to a local treatment plant, or remote properties not connected to the mains sewer, the foul water drainage pipes will need to connect to a sewage treatment plant on the property or a septic tank.

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What is the difference between foul water and surface water drainage?  

A surface water drainage system transports rainwater that runs off from roofs that is collected in gutters and from driveways and is taken to either a soakaway, to a watercourse or into a surface water sewer. Generally, this type of water is less contaminated than foul water and so does not require the same treatment.


What is a combined drainage system?

In some older buildings, a combined sewer may have been used where both foul water and surface water channelled through the main sewer system. A surface water sewer should only ever carry surface water (rainwater that has been collected) to avoid untreated foul water being discharged into the environment. The problem with combined drainage systems is that when it rains and volumes of water increase, the system may not be able to cope. Ultimately this may result in contaminated foul water being discharged into the environment to prevent flooding of homes.


What are the key components of a foul water drainage system?

A foul water drainage system will include gravity foul water drainage pipes and standard fittings including couplers, bends and junctions. It will also include inspection chambers where there is a change of direction or size of pipework, at the start of a drainage run, at a change in gradient or at a junction.


What are the regulations for foul water drainage design?

The foul water drainage system can be private drainage pipework around a single property, or it can be an adoptable sewer if the pipework is serving two or more properties.

Regulations for private drainage:

In England & Wales, Part H (Drainage and Waste Disposal) of The Building Regulations outlines the guidelines for drainage and waste disposal that must be met.
In Scotland, The Building (Scotland) Regulations apply.

Regulations for adoptable sewers:

In England, Ofwat’s Sewerage Sector Guidance, Appendix C of the Design & Construction Guidance (DCG) now applies, and this replaces all editions of ‘Sewers for Adoption’.
In Wales, Sewers for Adoption 7th Edition remains the current guidance for sewer Adoption.
In Scotland, Sewers for Scotland v 4.0 applies.

Gravity Sewer

Gravity feed is the most common way to transport sewage. Wavin offers you a complete range of PVC and PP pipes, smooth and structured wall pipes and associated fittings with secure push-fit joints for gravity-fed sewage transport.

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Inspection Chambers

To ensure high performance of sewerage systems, they must be inspected and maintained. Wavin offers a wide range of deep and shallow Inspection Chambers for safe and easy access.

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