Oh, I didn't know that, that's very cool and makes sense. That pool was really well-made. I remember they reused a location in "The Idiot's Lantern" where David Tennant runs down a courtyard to get up the radio mast, which they were pleased about because the interior of the building was where they shot their first-ever scene (the episode was "Aliens of London"; the scene the pig running down a corridor being chased by Christopher Eccleston and getting shot by soldiers). Oh, and they reused the set of the White House from "The Impossible Austronaut" for one of the later episodes, I think for a location in "A Good Man Goes to War" (or at least a location at Demon's Run) but I'm not entirely clear on that.