Polymer materials that are used in outdoor enviroments are exposed to humidity and polution. In addition, some insulation materials installed in water or embeded to slush containing serious pollutants for a long time. These conditions adversely affect the dielectric properties of insulating materials. In this study, the prepared unsaturated polyester (UPE) samples are stored in an ionized water solution for 8, 24, and 168 hours. This ionized water solution is considered to represent the polluted water in the outdoor environments. Further, the dielectric behaviors of the prepared polyester samples are investigated using the inclined plane test (IPT) method, whereas the leakage current data that are recorded during the experiment are analyzed using the recurrence plot (RP) method. The results of applying the inclined plane test on the unsaturated polyester samples depict that the lifetime of the samples decreased with an increase in the period of storage in the ionized water solution. Further, the results of the recurrence plot analysis reveal that the recurrence plot point density also depicted a decrease with an increase in the period of storage in the ionized water solution.