Abstract: An ultra-violet absorbence-based monitor for on-line monitoring of organic pollution in water at on-site locations measure the reduction in UV light passed through a sample and also makes measurements to provide indications of the amounts of visible light absorbed by, and scattered by, the samples respectively. The amount of organic matter is determined from the measured reduction in UV light by a calculation in which the results of the other measurements are used for compensation purposes. The sampling apparatus comprises a buoyant sampling head with an inlet port submerged beneath the water surface.