A. Development by a water authority for the purposes of their functions consisting of—
(a)development not above ground level required in connection with the provision, improvement, maintenance or repair of a sewer, outfall pipe, sludge main or associated apparatus,
(b)development not above ground level required in connection with the supply of water or for conserving, redistributing or augmenting water resources, or for the conveyance of water treatment sludge,
(c)development in, on or under any watercourse or land drainage works and required in connection with the improvement or maintenance or repair of that watercourse or those land drainage works,
(d)the provision of a building, plant or machinery or apparatus in, on, over or under land for the purpose of survey or investigation,
(e)the maintenance, improvement or repair of works for measuring the flow in any watercourse or channel,
(f)the installation in a water distribution system of a booster station, valve house, meter or switch-gear house,
(g)any works authorised by or required in connection with an order made under section 1 or 2 of the Drought Act 1976(1),
(h)any other development in, on, over or under their operational land, other than the provision of a building but including the extension or alteration of a building.
A.1 Development is not permitted by Class A if—
(a)in the case of any Class A(b) development, it would include the construction of a reservoir,
(b)in the case of any Class A(f) development involving the installation of a station or house exceeding 29 cubic metres in capacity, that installation would be carried out at or above ground level or under a highway used by vehicular traffic,
(c)in the case of any Class A(h) development, it would consist of or include the extension or alteration of a building so that—
(i)its design or external appearance would be materially affected, or
(ii)the height of the original building would be exceeded, or the content of the original building would be exceeded by more than 25%, or
(iii)the floorspace of the original building would be exceeded by more than 1,000 square metres, or
(d)in the case of any Class A(h) development, it would consist of the installation or erection of any plant or machinery exceeding 15 metres in height or the height of anything it replaces, whichever is the greater.
A.2 Development is permitted by Class A(d) subject to the condition that, on completion of the survey or investigation, or at the expiration of 6 months from the commencement of the development concerned, whichever is the sooner, all such operations shall cease and all such buildings, plant or apparatus shall be removed and the land restored as soon as reasonably practicable to its former condition (or to any other condition which may be agreed with the local planning authority).