Determination and Classification of Qanat Water Quality Based on Groundwater Quality Indices in East of Tehran, Iran

Background: Qanat is a valuable source of groundwater, the maintenance of which requires quantitative and qualitative monitoring. Since the qanat water is currently used in some parts of Iran for drinking and agricultural purposes, its quality management is of great importance. This study aimed to evaluate the water quality of the qanat in the eastern areas of Tehran. Methods: Water sampling was performed in eight qanats in the east of Tehran in triplicate (mother well and one of the access shafts and outlet) during the summer of 2020. The measured parameters were pH, total dissolved solids (TDS), electrical conductivity (EC), CO3 2-, HCO3 - , Na2+, Ca2+, Mg2+, K+, Cl- , NO3 , SO4 2-, total hardness (TH) and total alkalinity (TA). The quality was assessed according to the standards introduced by the World Health Organization (WHO) and Food and Agriculture Organization. Groundwater quality index (GWQI) was used to classify the samples. Results: The lowest (56.05) and the highest (2058.58) GWQI scores corresponded to qanats 5 (Elimon) and 8 (Aminabad) with good and very poor quality, respectively. There was a decrease in the water quality of qanats 8 (Aminabad), 7 (Sulaymaniyah), 6 (Mehdiabad) and 2 (Majidieh), respectively. Conclusion: The quality of the qanats were in the range of good to very poor. The reasons for difference in water quality could be due to the direction of anthropological pollutants and geological structures. To control the water quality of the qanats in the east of Tehran, the quality monitoring network is recommended to be designed for various pollutants and optimized for long term.