Abstract: A unit for treating liquid comprises a cylindrical container (1) which, in an upper chamber (6), has a set of slender tubes (8) which the liquid is forced to pass on its way from an inlet (10) to an outlet (9), so as to be subjected to a treatment, such as deionization, during this forced passage. An annular casing (11) is arranged in a lower chamber (7) and serves to distribute the liquid flowing in through the inlet (10). The casing (11) is defined by inner and outer side walls (12, 13) sealingly interconnected along an upper edge portion (14) as well as interconnected by at least one lower, transverse wall (15) which is provided with a plurality of small holes through which the liquid is squeezed out in the form of a large number of individual jets. The cross-sectional area of the liquid-distributing casing (11) continuously decreases away from the inlet (10) towards an opposite end (18) of the casing.