Assessment of Tigris River Water Quality for Drinking and Domestic Use in the post-war city of Mosul by using the Canadian Environment Water Quality Index CCME-WQI and Heavy Metal Pollution Index HPI

River water quality is highly sensitive to human activities such as urbanization, industrialization, and agriculture. It is even more susceptible to significant and prolonged changes, such as those caused by wars, which degrade surface waters and impair their use for drinking, industrial, agricultural, recreational, and other purposes. To assess the impact of the war in Mosul on the quality of the Tigris River’s water, the Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI) was used. A total of 120 water samples were collected along the river in four series during 2022 and 2023. The study revealed that in most riparian sites the Tigris River had higher levels of heavy metals (Cd, Pb, Cr, Ni) than permitted by WHO standards (2004), with exception of Zn. Zone 3 exhibited the highest level of pollution. Significant seasonal and annual variations were observed in most parameters, except pH and sulfate (SO₄²⁻), due to geological and debris-related factors. Based on CCME WQI, water quality dropped from 85.8 in 2014 (pre-war) to 68.8 in 2022, then slightly improved to 73.25 in 2023, classifying the river as “Fair.” HPI values indicated good quality at sites S1–S3, while sites S4–S10 were unsuitable. The pollution ranking by metal was: Cd > Pb > Ni > Cr > Zn. Cd and Pb pose a very high ecological risk due to their high bio accumulative potential in the Tigris river.