To lower the loss by conversion to electric power and improve the energy efficiency by driving a pump, which pumps up sea water, by transmitting driving force of a driving source through a transmitting means to the pump and driving a power generator by the driving force transmitted through a transmitting means.

A diesel engine 4 which is a driving source of this water producing apparatus 1 is connected with a power generator 5 and a high pressure pump 6 through a clutch 3 and the clutch 3 selectively drives either the power generator 5 or the high pressure pump 6 by switching operation. That is, the high pressure pump 6 is driven by a diesel engine to operate the water producing apparatus 1 and by switching the clutch 3, the power generator 5 is driven by the diesel engine 4. To carry out water producing treatment, sea water 7 is pumped up by the high pressure pump 6 and desalinated by a reverse osmosis membrane 8 to obtain drinking water 9. On the other hand, in the case that the power generator 5 is driven, the driving force of the diesel engine 4 is transmitted to the power generator 5 and obtained electric power is sent to heaters and luminaires 11.