Abstract: This invention relates to apparatus and methods for the treatment of fluids with magnetic fields and, in particular, to the disinfection of contaminated fluids by treating the fluids with a high-gauss magnet followed by ultraviolet radiation. Fluids can accumulate organic and non-organic contaminants from multiple and diverse sources. Magnetic treatment enhances the ability to separate hydrophobic contaminants from the fluid and the ability of that fluid to be disinfected. A wide variety of fluids can be treated with these methods including water to be made potable, industrial water and other fluids such as coolants and lubricants, oils, petrochemicals such as fuels, and beverages. Further, fluid can be exposed to UV radiation at a flow rate sufficient to prevent occlusion of UV-transmissible surfaces in the disinfection system by contaminants in the fluid or by removing a set amount of those contaminants.