38.—(1) For the purposes of water undertakings development of any of the following descriptions—
(a)the laying underground of mains, pipes or other apparatus;
(b)the installation in a water distribution system of a booster station, valve house, meter or switchgear house;
(c)the provision of a building, plant, machinery or apparatus in, on, over or under land for the purpose of survey or investigation;
(d)any other development carried out in, on, over or under the operational land other than the provision of a building but including the extension or alteration of a building.
(2) Development is not permitted by this class if—
(a)it would include the construction of a reservoir;
(b)in the case of any development referred to in sub-paragraph (1)(b) involving the installation of a booster station or valve house exceeding 29 cubic metres in capacity, that installation is carried out at or above ground level or under a road used by vehicular traffic;
(c)in the case of any development referred to in sub-paragraph (1)(d), 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;
(ii)the height of the original building would be exceeded, or the cubic content of the original building would be exceeded by more than 25%; or
(iii)the floor area of the original building would be exceeded by more than 1,000 square metres; or
(d)in the case of any development referred to in sub-paragraph (1)(d), 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.
(3) Development is permitted by sub-paragraph (1)(c) 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, whichever is the sooner, all such operations shall cease and all such buildings, plant, machinery 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 planning authority).