A dehydrating system is designed to maintain the availability of a plant having the dehydrating system using a water separation membrane by allowing a water separation membrane unit to be replaced while the plant is in operation. The dehydrating system comprises at least two water separation membrane units in use arranged parallel to the direction of flow of a fluid to be processed, is configured so that at least one spare water separation membrane unit can be installed parallel to the direction of flow of the fluid to be processed with respect to the at least two water separation membrane units, having monitoring devices for the product fluid to be taken out, and maintains the properties of the product fluid by operating the spare water separation membrane unit depending on the properties of the product fluid monitored by the monitoring devices.