Abstract: The present invention is directed to a novel method for analyzing aqueous systems to simultaneously quantify the concentrations of multiple active or inactive treating components which may be contained therein. The method comprises determining the absorbance or emission spectrum of the components in the aqueous system over the wavelength range of from 200 to 2500 nm, and then applying chemometrics algorithms to extract and analyze features in the spectrum that are specific to the qualitative and quantitative concentrations from the specific components to simultaneously determine the concentrations of the components.