Abstract: Connected in a water circuit for cooling or heating gaseous fuel in a fuel system for a gas turbine plant is a gas/liquid separation apparatus which serves to separate gases contained in the water from the water, and to detect them. The container of the separation apparatus is split up by a partition into a water entry chamber and a water exit chamber. The incoming water flow is split up in the water entry chamber into an upward-flowing and a downward-flowing water flow. Located above the water is a gas-filled space into which gas bubbles disperse. The upward-flowing water flows over an overflow weir, and the downward-flowing water flows into the water exit chamber through openings in the lower region of the partition. The separation apparatus thus includes a calm, free water level in the water entry chamber, and an irrotational flow from the water exit chamber.