Process for purifying a stream comprising phosphoric acid and a first amount of impurities, wherein: a slurry of phosphoric acid crystals in a water mother liquor is formed; the phosphoric acid crystals are separated from the mother liquor by filtration in a wash column comprising at least one filtering element (4), while a packed bed of crystals coming from the slurry forms near said filtering element (4); the separated phosphoric acid crystals are washed in the wash column by bringing a washing liquid in countercurrent to the crystals in the bed up to a wash front, where the washing liquid recrystallizes, the bed being subjected to a movement in the direction of said wash front (6b); a purified stream comprising phosphoric acid and a reduced amount of impurities is formed by melting at least part of the washed crystals; the purified stream is extracted from the wash column through a product outlet of the wash column; characterized in that water is introduced into said wash column (1), between the wash front (6b) and the product outlet and/or in a melting circuit (8,10,11,21) producing at least part of the washing liquid, and wherein the introduction of the said water decreases the equilibrium temperature of the contents of the melting circuit (8,10,11,21).