To provide a method for treating a fluid, particularly an aqueous fluid to kill bacteria in a conduit and cause flocculation of a suspended solid matter.

The apparatus for treating a fluid in the conduit includes first and second core elements 11 and 12 of magnetically conductive material surrounding the conduit adapted to be mounted to the conduit 10 surrounding the conduit at spaced positions along the conduit 10 and means for establishing radio frequency magnetic fluxes in the core elements, for generating respective electromagnetic fields in the fluid to be treated extending from spaced positions along the conduit.