Technical Booklet C Site Preparation and Resistance to Contaminants and Moisture·Page 8·27
Subsoil drainage
The site and adjacent ground must be drained or the building otherwise protected to prevent harmful effects from groundwater and existing subsoil drainage on the building or occupants' health.
The site of a building and the ground adjacent to it shall be drained as far as reasonably practicable, or the building otherwise protected so as to prevent any harmful effect on the building or the health of the occupants caused by—
(a) ground water; and
(b) existing subsoil drainage.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet C - Site Preparation and Resistance to Contaminants and Moisture.pdf