As its name suggests, Tower Windmill was once a working mill. Dating from 1798, the windmill was built by the first Lord Melbourne at a cost of £250 to grind local grain. This style of windmill was developed in the C18th and featured a domed top to which the sails were attached. The dome was designed to revolve, in order to take advantage of the wind irrespective of the direction from which it was blowing. The turning of the sail powered a series of gears, which in turn drove the millstones which ground the grain.
Grain continued to be milled here until the late C19th, when the windmill became disused and gradually fell into disrepair. When the new reservoir was constructed, it was planned to convert the tower into a viewing platform overlooking the water, but the building was found to be unsuitable and the conversion was never completed.