Previously called Priory Flatte, in c.1970 it became a water training centre and had a modern extension of bedrooms added for the students. In the grounds there was a mock sewer for confined spaces training and I think a grid of pipework for leak detection training. The House, bedrooms and workshops were demolished c. 2001 for a new housing estate. It is rumoured that all that remains is the wood panelling that was in the hall and stairwell. Apparently this taken to Over Burrows House near Brailsford, where it remained until at least April 2021 when it was listed in an auction selling off the entire contents of Over Burrows House.
Photo is from Peter Cholerton who says: Millis House was probably named after Sir Leonard William Francis Millis, CBE (1908–1986), who for many years was the secretary of the British Waterworks Association. He was knighted in 1977.