Requirement
Separate systems of drainage
H5. Any system for discharging water to a sewer which is provided pursuant to paragraph H3 shall be separate from that provided for the conveyance of foul water from the building.
Limits of application
Requirement H5 applies only to a system provided in connection with the erection or extension of a building where it is reasonably practicable for the system to discharge directly or indirectly to a sewer for the separate conveyance of surface water which is:
(a). shown on a map of sewers; or
(b). under construction either by the sewerage undertaker or by some other person (where the sewer is the subject of an agreement to make a declaration of vesting pursuant to Section 104 of the Water Industry Act 1991 (b)).
(b) Section 104 was amended by Section 96 of the Schedule 9 to the Water Act 2003. and is prospectively amended by Section 42 of the Flood and Water Management Act 2010 (c. 29).
Introduction to provisions
0.1 These provisions are to help minimise the volume of rainwater entering the public foul sewer system as this can overload the capacity of the sewer and cause flooding.
Provision where separate sewer systems are provided
1.1 Where the buildings are to be drained to the public sewer system, and the sewerage undertaker has provided a separate system of sewers, separate drainage systems will be necessary in order to comply with the requirements of Section 106 (Right to communicate with public sewers) of the Water Industry Act 1991 (see appendix H1-C paragraph C.7).
Provision where separate sewer systems are proposed
1.2 Separate foul and rainwater drainage systems should also be provided where there is a combined sewer system at present but a system of sewers which provides for the separate conveyance of surface water is under construction either by the sewerage undertaker or by some other person (where the sewer is the subject of an agreement to make declaration of vesting pursuant to Section 104 of the Water Industry Act 1991).
1.3 These separate drainage systems will both initially connect to the existing combined sewer system. However, when the separate sewer systems are completed, the drainage will be reconnected to the new sewers, minimising the disruption to the occupiers.
Contaminated runoff
1.4 Approved Document H3 paragraph 3.21 deals with drainage from areas where materials are stored which could contaminate runoff. This could cause pollution if discharged to a surface water sewer. Where such flows are to be discharged into the foul sewer system, the consent of the sewerage undertaker should first be obtained in accordance with Section 106 (Right to communicate with public sewers) of the Water Industry Act 1991 (see appendix H1-C paragraph C.7). The sewerage undertaker should also be consulted where such flows are to be discharged into a foul drain which, though it would initially connect to a combined sewer, is intended would eventually be reconnected to a proposed foul sewer.
