Fuente: WIPO "tomato" The present invention relates to a fiber material, and its use in installations that purify water, wherein the fiber material comprises a multitude of free polymorphic fibers, wherein at least 95% of the fibers have a particle size between 0.01 and 25 mm, and wherein the fibers are obtained by shredding or grinding a stone wool substrate that is suitable for use in the hydroponics of crops. The invention also relates to a method for purifying water and a device provided with the fiber material as described herein for treating water.