Development for the purposes of their undertaking by statutory undertakers for the supply of water or hydraulic power consisting of—
(a)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,
(b)development in, on or under any watercourse and required in connection with the improvement or maintenance of that watercourse,
(c)the provision of a building, plant, machinery or apparatus in, on, over or under land for the purpose of survey or investigation,
(d)the maintenance, improvement or repair of works for measuring the flow in any watercourse or channel,
(e)the installation in a water distribution system of a booster station, valve house, meter or switch-gear house,
(f)any works authorised by or required in connection with an order made under section 73 of the Water Resources Act 1991(1) (power to make ordinary and emergency drought orders),
(g)any other development in, on, over or under operational land other than the provision of a building but including the extension or alteration of a building.