Abstract: A fluid treatment device, especially for reducing or removing the effects of hard water, has a fluid inlet, a fluid outlet, and a cavity extending between the inlet and the outlet. A dielectric channel separator (preferably of plastics material, more preferably PTFE) is located in the cavity between the inlet and the outlet and extends at least part way along the cavity. The dielectric channel separator divides thecavity into a plurality of elongate channels which are mutually coextensive for at least part of their length in the direction of fluid flow from the inlet to the outlet and are at least partially bounded by dielectric material. A metallic channel separator, preferably of zinc, can also be provided to provide a degree of protection against corrosion. The channel separators are preferably configured to encourage turbulence in the fluid flowing through the device.