Apparatus for treating liquid by contact with a particulate adsorbent material comprises a regeneration chamber (10) within a reservoir (2) for liquid to be treated. Adsorbent material is recycled along a path including passage through the regeneration chamber (10) and in a body of liquid in the reservoir to contact and treat the liquid. The adsorbent material is capable of regeneration, and the regeneration chamber (10) is defined between two electrodes (36, 38), which can be coupled to a source of electrical power. The treatment process can be continuous with liquid flowing through the reservoir while the adsorbent material is recycled and regenerated. Alternatively, individual quantities of liquid may be treated on a batch basis. A plurality of regeneration chambers may be arranged within a common reservoir, such as in a bank of chambers aligned along an axis thereof.