The goal of this study is to determine the relationship between transient changes in total oxidizable carbon concentration (TOC), bacterial numbers, and endotoxin concentrations at several serial unit operations in a high purity water system. Bacteria are a dynamic component of any ambient temperature sections in a high purity water system; they are living and growing inhabitants. Their numerical variability over time poses challenging QA/QC problems for many industries using high purity waters for manufacturing, formulation, equipment rinsing, and medical device preparation. Preliminary data (Husted et al., 1994) suggested that a possible relationship existed between spontaneous transient elevations in TOC concentration and total planktonic (free floating) bacterial numbers in high purity waters: rising TOC produced sudden increases in bacterial concentration. If the results collected earlier are reproducible, real time monitoring of TOC stability may offer a gateway measurement permitting estimation of changes in endotoxin and bacterial cell concentration, analyses currently made off line in the laboratory. This correlation would also supply guidance for system operation to produce water with both an enhanced and a reproducible quality.