Actually Judge, your bit about the Grand Union isn't strictly true. The Braunston summit pound is mainly supplied by Daventry reservoir (nr. Welton) and Drayton reservoir which is also in Daventry, but that summit pound is fairly short (Braunston top to Long Buckby top). There is another, longer summit at Tring. When building the canals, every watercourse, no matter how big, and land drain was diverted to the canal to ensure water supplies. If you drive around the Midlands, nearly every reservoir you see is for the canals. Although everyone sees them now as an old form of transport, in their time they were the greatest thing since sliced bread!, and absolutely reveloutionary. Boat skippers had the same kudos as an airline pilot today. As regards water usage, a narrow lock (7' x 72' x 6' approx) uses around 25,000 gallons a time (1000 bath fulls!). Wide locks use around 50,000 gallons. Since the canals were built there have been various pumping schemes to keep them supplied. The oldest in the world are the Crofton steam pumps on the Kennet & Avon canal, and to this day many of the more popular flights of locks have electric 'back pumping' systems to get water back to the top of the locks.