Environmental contamination concerns are driving the development of water-based paints. The stability of the dispersions is important and is closely related to product quality. These epoxy polyesters are studied using the Zetasizer Nano. At room temperature two different sample lots showed no indication of stability differences in both size and zeta measurements. At elevated temperature of 80C, however, one batch clearly exhibited longer stability than the other. This stability difference is in agreement with the user's observations seen on storage of the samples. The use of the Zetasizer Nano ZS allowed identification of the stability of the paint products to be determined on much shorter timescales than traditional tests, greatly increasing the efficiency of QA/QC processes.