A method for producing an iron-containing filter material for water treatment includes the steps of reacting a trivalent iron compound and a base inside a vessel until the trivalent iron is completely neutralized, to obtain an iron hydroxide and a salt consisting of the anion of the trivalent iron compound and the cation of the base; feeding the iron hydroxide and the salt into ceramic membranes to wash the iron hydroxide from the salt in cross-flow; feeding the iron hydroxide suspension to a membrane filter press where part of the water is removed, to obtain a panel having a moisture content of less than 77% by weight; inserting the panel into containers; and positioning the containers inside a refrigeration chamber operating at atmospheric pressure and at temperatures less than 0° C. for a time between 24 and 240 hours.