Ground waters may undergo a process of contamination in various ways, but the presence and amount of heavy metals in them can be indicative of their purity and usage. Apart from that, the heavy metals are among the most widely spread pollutants in nature, and their presence in groundwater indicates the existence of natural or anthropogenic sources of contamination. Ground waters polluted with heavy metals can also be very toxic and harmful to human health, and very damaging to the environment as well. In this article, the concentrations of eight toxic heavy metals (Fe, Mn, Cu, Al, Ni, Pb, Zn, Cr) were analyzed in the ground waters of the Mesta River Basin. A number of data for the concentrations of those heavy metals were used in order to calculate the following two indices describing groundwater purity: the Heavy Metal Pollution Index (HPI), and the Metal Index (MI). Both indices describe the overall quality of groundwater in direct relationship to the sum total of heavy metal concentrations. On one hand, minimal concentrations of heavy metals are necessary for the faultless functioning of organisms and indispensable to various biochemical processes, but on the other hand, in high concentrations, they might lead to dysfunctions in the cells of healthy organisms, and problems within their enzyme system. And these effects are entirely dependent upon the nature of the heavy metals involved. The research carried out so far shows that, according to HPI, about 65% of the shallow ground waters in the Mesta River Basin can be classified as being of excellent quality. The values obtained for the HPI are in the range of 3 to 64 (id est under the critical value of 100), or the groundwater is not contaminated with heavy metals. The MI varies within the range of 0.3 to 2.6, and therefore the groundwater from the zones with active water exchange can be characterized as being of slight to medium poor quality (41%), and the groundwater within Class II (or classified as pure with values of MI between 0.3 and 1.0) comprise approximately 59% of the overall catchment area.