A new instrument is available for on-line monitoring of nitrate and/or iron in water. This instrument uses absorbance spectrometry and highly advanced analytical algorithms to determine the presence and concentration of certain chemical components in solutions. The analytical technique uses the natural absorbance characteristics of a sample stream over a range of wavelengths without the need to physically alter the sample or the need to introduce any reagents into the sample line. The technology is capable of simultaneously analyzing several chemical constituents and of monitoring multiple sample lines. Although this technology was originally developed for use by NASA, it has since been demonstrated for use in water and wastewater applications, including the monitoring and control of several important water treatment processes. Information will be presented which will compare on-line analytical results obtained using this instrument with analytical results obtained using standard laboratory methods.