Watermills were an essential part of medieval life, providing flour, bran and crushed oats for the community and its livestock. The first mill to be built at Mapledurham was in the 15th century and its original roof and wall timbers still survive in the core of the present building. Probably a simple rectangular building of two storeys when first constructed, the Mapledurham Watermill would have had timber-framed walls and a thatched roof. The single water wheel would have been situated at one end.

In the late 17th century, coinciding with the time of the plague and great fire of 1666, the mill was enlarged to increase its capacity to deal with the exodus of the wealthy London gentry. It was extended to include an additional waterwheel, fed by a flume cut on the landward side, at the same time having the roof re-constructed to allow the housing of storage bins which could be efficiently supplied by a new sack hoist housed in a cupola. This doubled the mill's production as each waterwheel controlled a pair of stones, bringing the total to four. In about 1700 the mill was modified to include a downstream extension, containing 'flour dressers', which were used to separate out the fine white flour from the bran. Some years later in 1777, the mill was extended again, probably benefiting from the recovery of London's society and the capital's subsequent increased prosperity, and a barn raised on saddle stones was constructed along with a covered causeway to the main building. This would allow produce to be stored safely from both the elements and rodents until it was collected and taken up river by barge.

The decline of Mapledurham Watermill was to come in the late 18th century when the huge wheat producing capabilities of the American continent, were realised. The mill was then used to produce fodder for livestock but eventually fell into a state of decay, until it was lovingly restored to full working order in the latter half of the 20th century.

Flour is ground in a simple but efficient process involving a series of cogs connected at various intervals by vertical and horizontal shafts, to the waterwheel. The waterwheel constructed in oak with elm paddles is rotated by fast flowing 'undershot' water, from a controllable sluice gate. A large cog called a 'pit wheel' is set in parallel to the waterwheel, along a horizontal shaft, with a further cog called a 'wallower', set at a right angle to it. This arrangement effectively transfers the turning motion from the horizontal shaft to a vertical one. A large 'spur wheel' is located higher up on the shaft which drives two small cogs called 'stone nuts', and these in turn drive spindles which turn the grinding (running) stones. At the top of the vertical shaft a final cog called a 'crown wheel' is located, which drives the sack hoist.

Together with Mapledurham House the mill is regularly open to the public. Visitors are encouraged to explore the workings of the mill and there are always millers on hand to explain the whole process. For those with a love of mechanical things, this mill provides a fascinating spectacle.