The study focused on the assessment of sources responsible for an urban riverâs water quality. To do the analysis, water samples were collected from three sources. The first source was rainfall, the second source was a Wastewater Treatment Plant (WWTP) which releases pre-treated wastewater in the river, and the third source was the river itself at upstream and downstream parts from the WWTP discharge point in the river. The results of the chemical analysis performed on those water samples showed that the water discharged from the WWTP into the river has a poor physico-chemical quality and high microbiological pollution. However as expected, water samples of rainfall were of good quality. Water samples from the river revealed the presence of microbiological flora (total coliforms, fecal coliforms, Escherichia coli and fecal Streptococci) and chemical elements such as ammonium (NH4+), manganese (Mn), nickel (Ni) with high concentrations values than those recommended for irrigation waters as defined by World Health Organization (WHO) and the Food and Agriculture Organization (FAO) of the United Nations. However, parameters like temperature (T°), hydrogen potential (pH), electrical conductivity (EC), total dissolved solids (TDS), suspended solids (SS), chemical oxygen demand (COD), biological oxygen demand (BOD5) ortho-phosphate (PO43-), nitrate (NO3-), nitrite (NO2-), sodium (Na+), bicarbonate (HCO3-), calcium (Ca2+), magnesium (Mg2+), chloride (Cl-), zinc (Zn2+) and iron (Fe2+) are in line with the reference values for irrigation. Furthermore, water mixing analysis model "End Members Mixing Analysis (EMMA)" based on principal component analysis (PCA) of physico-chemical parameters of the pre-treated wastewater from the WWTP discharged into the river, the rainfall, and the river collected at upward of WWTP junction discharge point in the river has been developed. The results show that the wastewater pre-treated by the WWTP and discharged into the river contributes to 13.72% of the river water chemistry compared to 33.64% for rainfall and 52.64% for river water before its junction with WWTP. This study revealed that during rainy season, Houet river has high concentrations of NH4+, metallic trace elements (Mn, Ni) and significant microbiological pollution due to (i) the discharge into the river of incomplete treated wastewater coming from the WWTP (ii) but also to the river itself, which minor bed is the depository of urban and domestic wastes. It is true that the river water quality is globally good for market gardening, but to ensure its long-term quality, authorities in charge of water resources and agriculture should (i) monitor and optimize WWTP wastewater treatment efficiency, (ii) and control/limit agricultural and domestic activities with potential pollution risks alongside the river.