The purpose of this work was to evaluate the long-term stability of a previously validated fat-water phantom under a range of environmental conditions. Two separate phantoms were constructed, each with a range of fat concentrations. The first phantom was subjected to three different temperature conditions over one year. The second fat phantom was kept at room temperature and studied over three years. Our results show that the fat-water phantom has excellent long-term stability at room temperature and is robust to different temperature conditions.