When dealing with open evaporative cooling water systems, there are two performance parameters of primary concern: corrosion and fouling. On-line monitoring of either would appear to be independent. By dividing the various forms of corrosion and fouling into subsets, interdependency can be established. This analysis, combined with the real-time dynamics of the cooling system, provides a link between key performance indicators (KPI) and key operating indicators (KOI). The real-time linkage can be harnessed to stepwise adjustments of controlled parameters such as blowdown, pH, oxidant, non-oxidizing biocides, dispersants, deposit control, and corrosion control additives in order to maintain corrosion and fouling within their respective user defined control ranges.