District heating system, comprising a primary water circuit that is coupled to a district heating network (FN) and has, connected thereto on the customer side, a hot water supply pipe (V) and a cold water return pipe (R), said system also comprising a secondary water circuit that is coupled to the customer-side heating system, wherein each water circuit is arranged in a customer-side premises , wherein the district heating system comprises a monitoring device, the monitoring device having: a detection device used to detect water loss from the primary water circuit in the customer-side premises , a reporting device designed to send alarm messages to a service and to a customer-side operating device of the district heating system when water loss is detected, controllable valve devices which are arranged between the primary water circuit and the district heating network and are designed to separate the primary water circuit from or connect the primary water circuit to the district heating network, wherein the valve device which opens and closes the hot water supply pipe (V) in the primary water circuit is located closer to the district heating network (FN) in the upstream direction in the hot water supply pipe (V) than other water-guiding fittings of the primary supply pipe (V) of the customer-side district heating system, wherein the valve device which opens and closes the cold water return pipe (R) in the primary water circuit is closer to the district heating network (FN) in the downstream direction than other water-guiding fittings of the primary return pipe (R) of the customer-side district heating system; wherein the monitoring device is also designed to control the valve devices in the customer-side premises in such a way that said devices separate the primary water circuit from the district heating network (FN) when water loss is detected. a detection device used to detect water loss from the primary water circuit in the customer-side premises , a reporting device designed to send alarm messages to a service and to a customer-side operating device of the district heating system when water loss is detected, controllable valve devices which are arranged between the primary water circuit and the district heating network and are designed to separate the primary water circuit from or connect the primary water circuit to the district heating network, wherein the valve device which opens and closes the hot water supply pipe (V) in the primary water circuit is located closer to the district heating network (FN) in the upstream direction in the hot water supply pipe (V) than other water-guiding fittings of the primary supply pipe (V) of the customer-side district heating system, wherein the valve device which opens and closes the cold water return pipe (R) in the primary water circuit is closer to the district heating network (FN) in the downstream direction than other water-guiding fittings of the primary return pipe (R) of the customer-side district heating system; wherein the monitoring device is also designed to control the valve devices in the customer-side premises in such a way that said devices separate the primary water circuit from the district heating network (FN) when water loss is detected. <EOS>