Removal of cell growth from a body of water

A method for the removal of bacteria, microbes and other cell growth from a body of water comprising sequentially applying an electromagnetic field of varying frequencies and ranges to a section of pipe or similar conduit communicable with the body of water as water passes therethrough for the purpose of inhibiting or removing said bacteria, microbes or other cell growth from said water wherein the application of the electro magnetic field to said section of pipe is achieved by magnetizing an element or elements comprising elongate strips of ferrite material positioned on an outer wall of the pipe or conduit and extending lengthwise of the axis of the pipe to create multiple overlapping magnetic fields.