University of Central Florida (UCF) is currently conducting a large-scale pilot study to determine the effect of blending different source waters on distribution systems water quality as a part of AWWARF and Tampa Bay Water tailored collaboration project (TBW project). In this study, finished waters from seven different processes are blended in varying ratios before distribution to eighteen pilot distribution systems (PDS) and various chemical and biological water quality parameters are monitored for a total of 12 months. This paper addresses surface characterization of aged unlined cast iron pipe, development of equilibrium model, comparison of model prediction and pilot observations. Includes 10 references, tables, figures.