A drain carrying ‘surface water’ i.e. rainwater. Surface water drains may discharge either to a soakaway, watercourse or surface water sewer.
In newer properties surface water and foul water are kept apart in separate drains. This is known as a separate drainage system. With this method, foul air is not created in the surface water drains. Older properties frequently have ‘combined drainage’ where surface water is discharged into the foul drains. Rainwater pipes should discharge to foul drains via gully traps, to stop foul air escaping from the drains.
It is extremely important to ensure that foul water is not discharged into a surface water drainage system. A survey will check that surface water drains are operating properly.