Disclosed fluid purification systems can comprise a treatment vessel configured to contain a fluid to be purified, a source of ultraviolet radiation with at least 50% of its emitted spectral energy at wavelengths between 315 nm and 400 nm positioned exterior to the treatment vessel, and a portion of a wall of said treatment vessel that is substantially transparent to the ultraviolet radiation emitted by the source of ultraviolet radiation, located so that at least 50% of the ultraviolet radiation propagates through the substantially transparent portion of the wall and is configured to propagate into fluid to be treated within the vessel for the purpose of killing or disabling pathogenic microorganisms in the fluid.
