A process for identifying the unit causing a raw water leak in a condenser of a thermal power plant consisting of n units, n being an integer comprised between 2 and 15, preferably between 3 and 8, characterized in that each of the n units is equipped with a cartridge intended to contain an ion-exchange resin in a volume comprised between 50 and 150 mL, advantageously between 80 and 120 mL, and in that it comprises the following steps: a) for each of the n units, purifying the ion-exchange resin intended to be placed in the cartridge; b) for each of the n units, placing the purified ion-exchange resin obtained at the end of step a) in the cartridge; c) for each of the n units, passing a volume of condensate comprised between 500 and 1 500 L, advantageously between 800 and 1 200 L, into the cartridge containing the purified ion-exchange resin placed during step b); d) for each of the n units, collecting the ion-exchange resin obtained at the end of step c); e) for each of the n units, regenerating the ion-exchange resin collected during step d) by elution using an aqueous regeneration solution; f) for each of the n units, collecting the eluate obtained at the end of step e) followed by determining the nature of the ionic species present in the eluate and the amount of each ionic species present in said eluate; and g) for each of the ionic species identified during step f), comparing the amounts of said ionic species determined in each of the n eluates. characterized in that each of the n units is equipped with a cartridge intended to contain an ion-exchange resin in a volume comprised between 50 and 150 mL, advantageously between 80 and 120 mL, and in that it comprises the following steps: a) for each of the n units, purifying the ion-exchange resin intended to be placed in the cartridge; b) for each of the n units, placing the purified ion-exchange resin obtained at the end of step a) in the cartridge; c) for each of the n units, passing a volume of condensate comprised between 500 and 1 500 L, advantageously between 800 and 1 200 L, into the cartridge containing the purified ion-exchange resin placed during step b); d) for each of the n units, collecting the ion-exchange resin obtained at the end of step c); e) for each of the n units, regenerating the ion-exchange resin collected during step d) by elution using an aqueous regeneration solution; f) for each of the n units, collecting the eluate obtained at the end of step e) followed by determining the nature of the ionic species present in the eluate and the amount of each ionic species present in said eluate; and g) for each of the ionic species identified during step f), comparing the amounts of said ionic species determined in each of the n eluates. a) for each of the n units, purifying the ion-exchange resin intended to be placed in the cartridge; b) for each of the n units, placing the purified ion-exchange resin obtained at the end of step a) in the cartridge; c) for each of the n units, passing a volume of condensate comprised between 500 and 1 500 L, advantageously between 800 and 1 200 L, into the cartridge containing the purified ion-exchange resin placed during step b); d) for each of the n units, collecting the ion-exchange resin obtained at the end of step c); e) for each of the n units, regenerating the ion-exchange resin collected during step d) by elution using an aqueous regeneration solution; f) for each of the n units, collecting the eluate obtained at the end of step e) followed by determining the nature of the ionic species present in the eluate and the amount of each ionic species present in said eluate; and g) for each of the ionic species identified during step f), comparing the amounts of said ionic species determined in each of the n eluates.