This study evaluated the spatio-temporal water quality of the Ismailia Canal, the primary drinking water source for the Suez Canal governorates, which is significantly impacted by surrounding agricultural (63%) and urban (27%) land use. The research aimed to assess the formation of carcinogenic Trihalomethanes (THMs) during pre-chlorination to help optimize disinfection protocols. Physicochemical parameters including Total Organic Carbon (TOC), heavy metals (Fe, Mn, Pb), and THMs, were analyzed in 32 raw and treated water samples collected from eight water treatment plants (WTPs) during the 2024 winter and summer seasons. GIS-based land-use mapping and multivariate statistical analysis (Pearson correlation and HCA) were employed to identify pollution drivers. Results indicate a spatial decline in raw water quality, with Total Dissolved Solids (TDS) increasing downstream due to cumulative pollution. Raw water Iron (Fe) concentrations consistently exceeded the 0.3 mg/L Egyptian standard. Treated water THM levels ranged from 40.50-82.10 mu g/L in winter and 24.50-68.22 mu g/L in summer. While the cumulative non-carcinogenic Hazard Index (HI) remained below 1.0, the lifetime incremental cancer risk (CRtotal) exceeded the 10-4 benchmark at several downstream WTPs, driven by dermal and inhalation exposure. Statistical analysis revealed strong associations between heavy metals, TOC, and turbidity, especially in summer, indicating that higher temperatures and agricultural runoff accelerate the formation of halogenated by-products through metal-organic complexation. These findings highlight the urgent need for stringent source water protection and the optimization of disinfection processes. Implementing advanced pre-treatment and evaluating alternative disinfectants are essential to mitigate public health risks associated with chlorinated by-products.