Obviously for a paper mill to work water is needed. In the 17th century Father Imberdis, a Jesuit from the Auvergne region, wrote: « One must choose a region where the climate is mild because the stream must not freeze in winter nor dry up in summer. ». This would render the task of making paper impossible. About the quality of the water he added : «It has to be the best, the kind of water that is so crystal-clear that one can see the smallest grain of sand on the riverbed.» The river Sorgue offers all this. Hence why in the 18th century there were 4 mills at Fontaine de Vaucluse. Water provides both the energy for the mill and the ‘chemistry' for the production process. Harnessed by the head race, a narrow canal made of wood or metal, the water runs ‘beneath' the wheel, pushing the ‘albs' (wooden paddles) making it turn anti-clockwise. The Vallis Clausa mill wheel measures 7metres in diameter and 2 metres deep, and has 48 of these paddles.