The effects of sample storage on the Assimilable Organic Carbon (AOC) bioassay using Pseudomonas fluorescens strain P17 and Spirillum strain NOX have not been fully quantified to date, although it has been stated that samples can "probably be held for several days". Experiments were performed by splitting twenty-two samples after chlorine residual neutralization and pasteurization, and holding one half of the replicate samples at 4 degrees C for one week. Both raw water samples and distribution system samples were tested for effects due to storage. After one week, the samples were inoculated with P17 and NOX, and the AOC of the sample was determined. By comparing the AOC of samples that were not stored with samples that were stored, it was observed that after one week of storage, the AOC of the stored samples increased by approximately 65%. Of this 65% increase, an 80% increase was observed on P17 counts while nearly no difference was observed on NOX counts. Of the twenty-two samples tested, only one displayed a decrease in AOC after one week of storage.