This industrial hall is all that remains of the "machine" that supplied Mons with drinkable water from 1871, the year when the river Trouille was diverted. Designed by the architect Hubert and the engineer Celi Moullan, this impressive machinery of pipes and mains was built in metal and glass and forced the water from the valley level up to the town water tanks in the castle place yard. To source the water, Mons purchased two springs known as the "Mouse Hole" and "La Vallière," and the water was transported via hydraulic motor.