To effectively control TOC concentrations in the two reservoirs serving the Orange Water and Sewer Authority (OWASA), the sources of TOC must be known. This study used a simplified steady-state mass balance approach to compare the main sources of TOC in the University Lake and the Cane Creek Reservoir. The main TOC sources were the TOC which is directly loaded to the reservoirs from the watershed (allochthonous TOC) and the TOC which is produced in the reservoirs by algae generated as a result of nutrient influxes to the reservoirs (autochthonous TOC). To determine the allochthonous TOC load, existing TOC and flow data was used along with TOC data from the sampling program. The sampling program involved monthly sampling of the tributaries of the University Lake and Cane Creek Reservoir for TOC over a five-month period. The autochthonous TOC load was determined by estimating the amount of algae which would grow in the reservoir due to the existing nutrient loadings. The results of this study indicate that allochthonous TOC is the primary source of TOC in the reservoirs. The TOC load from the watershed accounts for 72 to 90 percent of the total TOC concentration in the reservoirs. The autochthonous TOC load accounts for only 10 to 28 percent of the in-lake TOC concentration.