Abstract: A device for treating water to reduce the concentration of cations or anions therein includes a water-tight container (4) of flexible material, designed to be able to lie substantially flat (FIG. 3) when empty and having an aperture (5) for the introduction of liquid, a strainer (7) extending across the aperture, and a closure (6) for the aperture, and a quantity of ion-exchange material (b 8) occupying a minor proportion of the available interior volume of the container. A soil extraction outfit and a soil testing outfit are described, which incorporate the water treatment device.