A method for treating drinking water by modifying the ion concentration in the filtered water by means of a replaceable cartridge filtering system comprises: —defining a plurality of types of water to be filtered on the basis of chemical and physical features of the water to be treated; —defining a plurality of classes of filtered water to be obtained with the filtering system on the basis of chemical and physical features of the filtered water; —providing a plurality of filter cartridges containing a filtering material based on a mixture of two or more ion exchange resins, the mixture being formed from predetermined proportions of the two or more resins, each cartridge of the plurality of cartridges having a different mixture of the two or more resins and being capable of retaining ions from, and/or releasing ions into, the water filtered in the filtration process; —correlating one or more of the classes of filtered water with each cartridge of the plurality of cartridges for each type of water to be filtered; —selecting a cartridge from the plurality of cartridges in order to obtain a desired class of filtered water on the basis of a specified type of water to be filtered.