Background and purpose: Nitrate and Nitrite are the pollutants of groundwater resources which are mainly associated with agricultural and wastewater disposal areas. Fluoride is beneficial to human health in proper doses. The aim of this study was to determine the spatial and temporal variations of nitrate, nitrite and fluoride in drinking water resources in Ilam, Iran, using Geographic Information System (GIS).

Materials and methods: This cross-sectional study was carried out in 20 drinking water sources in Ilam. The results of a 5-year archived analysis obtained from Water and Sewage Co was analyzed in GIS version 9.3 and SPSS version 16 applying one way ANOVA. Sampling was done according to the Standard method book.

Results: The best methods of interpolation for fluoride, nitrate and nitrite (considering the normal distribution of data) was ordinary Kriging and the Gaussian, exponential and spherical, respectively. Based on the maps, the highest values ​​of all parameters in most cases were found in central and eastern regions. The results of one way ANOVA showed a significant difference in average concentration of fluoride between different seasons (P= 0.025). Also, there were  significant differences in mean verification parameters measured in different seasons and different years (compared to all seasons) (P<0.001). The average level of nitrate in all sources were significantly lower than the international standard level of 50 milligrams per liter (P<0.001).

Conclusion: The results showed that in most regions the fluoride concentrations were lower than standard levels. According to the important role of fluoride on human health, authorities in Iran’s Ministry of Health should conduct programs for fluorination of water resources in low level area. To decrease the increasing rate of nitrate, some useful actions such as protecting the wells, construction of wastewater treatment plants, controlling the use of nitrogen fertilizers and continuous monitoring of water quality could be of great benefit.