Water quality and hydrochemistry of Tigris River in a metropolitan city: long-term assessment

This study focuses on the long-term estimation quality of the Tigris River at Baghdad City, Iraq, for a period of 14 years of observation data (2009–2022). An overall analysis of 20 physico-chemical factors from 12 sampling sites related to major water treatment plants was conducted. Multivariate statistical techniques were used to determine pollution sources and find out the most important parameters affecting river water quality. For assessing water suitability for irrigation, US Salinity Laboratory diagram was employed. Results illustrated that the quality of Tigris River water before treatment fluctuated between “poor” and “unsuitable” for drinking, with most samples classified as “very poor”. Factor analysis illustrated six major parameters that explained further than 75% of the total variation, highlighting the influence of natural hydrogeochemical processes, domestic and industrial discharges, and agricultural return flows. Hydrochemical evaluations showed that the control geochemical processes were dissolution of silicate, exchange of reverse ion, and weathering of carbonate. Despite its unsuitability for drinking without treatment, irrigation indices generally classified the water as “suitable” to “permissible” for agricultural use. To protect Baghdad's vital water supply, the Tigris River requires immediate pollution control and sustainable management. • Analyzed a comprehensive 14-year dataset (2009–2022) of 20 physico-chemical parameters from 12 sampling sites to evaluate the Tigris River's quality in Baghdad. • Determined through Water Quality Index (WQI) and geochemical indices that while the river water is "poor" to "unsuitable" for drinking without advanced treatment, it remains "suitable" for irrigation purposes. • Identified six major factors explaining over 75% of water quality variance, highlighting the critical impact of anthropogenic discharges (industrial/domestic) alongside natural hydrogeochemical processes like silicate dissolution and ion exchange. • Establishes a scientific basis for urgent pollution control and sustainable water management strategies to align with Sustainable Development Goal 6 (Clean Water and Sanitation).