The invention relates to filtering devices for purifying a liquid and can be used in household conditions for additional purification of mains water and other liquids for household needs. The filtering device consists of two working zones, at least, of one fixing means at least one adjusting element. The upper working zone is configured to enable an adjustment of the hardness value of the filtered liquid throughout the service life in the form of a container with the inner cavity filled with the filtering material configured with two groups of distributors of filtered liquid flows, where the adjusting element presents a conduit arranged in the upper working zone and a valve of the fixing means which is interconnected therewith during the liquid filtration process. The technical result: a filtering device based on gravity feed is created for purifying a liquid which provides for an even softening of the filtered liquid throughout the total service life of the device while maintaining the filtering capacity thereof (1 independent and 14 dependent claims of the claims, 10 figures).