Abstract: An apparatus for measuring the impurity content of drinking water processes has a monochromatic light source projecting a beam of visible light toward a light trap. A water sample generator passes a water sample transverse to and intersecting the beam of light. A photo sensor array with an angular resolution of at least 0.10° detects forward scattered light from particles in the water sample. A data acquisition and processing system connected to the photo sensor array receives signals of the intensity of scattered light as a function of the scattering angle and compares the received light intensities to stored patterns of known waterborne contaminants. Based upon detected contaminants and their concentrations, the data acquisition and processing system provides an output on a connector which can be used to control a water processing system to adjust treatment of drinking water for contamination such as bacterial pathogens.