To save water and stave off canal closure in drought conditions, some canal companies built sideponds alongside locks. A separate chamber connected to the lock by a culvert and paddle, they enabled a proportion of the water to be ‘re-used’. When emptying a lock, you would first open the side paddle and empty water into the sidepond, then when it makes a level, close the side paddle and empty the rest using the bottom paddles as normal. When you refill the lock, first fill it from the sidepond and then when it makes a level, close the side paddle and fill the rest from the top paddles. Very few are still operable, but often the remains of sideponds or their paddles can be seen – our picture shows double sideponds (which saved even more water) at Marsworth on the Grand Union. Where locks were paired (like at Hillmorton) there might be an interconnecting paddle enabling one lock to act as sidepond to the other – sometimes these, too, can still be seen.