A system for treating a medium, such as water, with ultraviolet light is provided. The system can include an ultraviolet treatment chamber that is shaped to reduce reflections of the ultraviolet light within the ultraviolet treatment chamber and/or improve absorption of the ultraviolet light by the medium. Furthermore, the system can add an agent to the medium within the treatment chamber to further treat one or more contaminants that may be present within the medium. Still further, additional treatment, such as filtering the medium with a permeable material can be implemented within the treatment system.