The concept nanofluids have attracted attention due to the possibility of gaining increments in transport properties including thermal conductivity. While such increments have been verified to some extent, their maintenance is a concern. Since the sustainability of the properties strongly depend on the colloidal behavior, a fundamental understanding on the dispersion stability of nanofluids is essential. This study is a demonstration of evaluating the dispersion stability of one-year old Alumina - Water nanofluids by means of the particle size distribution and zeta potential measurements. It is critical to report the thermophysical and particulate characteristics of nanofluids over certain periods, since such an approach will help on foreseeing the possibility of these fluids' transition to applications, as well as their feasible use in industry as heat transfer fluids. The zeta potential measurements on the samples indicate high electro-dynamic stability, while the particle size distribution analyses revealed a moderately poly-dispersed condition of nanoparticles. No nanoparticle settlement was detected through visual inspection. When compared to those reported in the literature, the aggregation observed in this study is not very critical. The authors highlight the requirement of performing stability experiments periodically and frequently. Also, some and give future work suggestions on nanofluid stability is provided.