Very interesting information StuartWaters. I can't see where the 'Wet Well' is at the Allington Lock area. Is it underground? I'm guessing it must be enormous?
On Google Earth:
From the tanks, follow the river towards Maidstone and just before you get to Ford's Wharf, there's a cross-shaped building, similar to a church when viewed from the air. That and the group of buildings adjacent to it comprise the Pumping Station. How much of that complex is still actually in use, I can't say. Southern Water have a habit of decommissioning plant but leaving it in place until its either in the way of something new or becomes dangerously derelict and needs demolition for safety reasons.
Considering that Central Maidstone, Allington and the surrounding area flows into it, I would say yes, it is quite large....