An apparatus for treating fluids with UV comprises a housing for receiving a flowof fluid having a fluid inlet, a fluid outlet, a reaction chamber, and at leasta first and second pair of UV sources located in the reactor chamber. The firstpair of UV sources has upper and lower UV sources that are positioned relativeto each other at a span that is greater than the span between the upper and lowerUV sources in the second pair. The second pair is positioned in either the upstreamor downstream flow of fluid. Subsequent UV sources or pairs of UV sources may beadvantageously used. The apparatus may be combined with a baffle arrangementwherein the baffles are preferably positioned to direct the fluid flow into thetreatment area.
