Abstract: In an apparatus for water treatment and comprising a pod containing a weakly acid or weakly basic ion exchanger and of which the inlet aperture is formed in the region of one end while the outlet orifice is formed in the region of the other end, in each case by a means which is permeable to liquid while retaining the ion exchanger, in order to render visible the fact that the ion exchanger is exhausted, there is in the region of the outlet orifice of the pod a chamber containing a strongly acid or strongly basic ion exchanger with a color indicator bonded thereon and the walls of which consist at least partially of a transparent material.