Pollution represents a serious problem for the environment. The aim of this research was to assess the level of organic pollution of the Ouémé River and his physical quality. Nine physical and chemical parameters were measured in nine different stations between March and October 2016, during dry and rainy season. The methods used were those recommended by the French Association of Normalization (AFNOR). Data were subjected to descriptive statistical analysis and multivariate statistical technics, including principal component analysis (PCA) and variance analysis. The Leclercq Organic pollution index was used to assess the level of organic pollution. The values of the measured parameters suggest an organic pollution on all stations. The pollution degree varies according to the study area with contents that sometimes pass those recommended by the WHO standards. More advanced information about water quality for this study area were obtained. Therefore, this study will help stakeholders to better manage Ouémé River’s water.

Difficulties of access to public water distribution sources in the suburbs of the sixth district of Cotonou create more resorts to the traditional water sources (wells). To assess the degree of chemical pollution of those waters, a study was conducted during the long rainy season of 2015 on thirty (30) traditional wells. Concentration of nitrogenous pollutants (nitrates and nitrites) was analyzed by cadmium reduction method and diazotization method, respectively. Micropollutants (lead and mercury) were respectively determined by the rapid extraction method of LeadTrak ™ column and by pre-concentration at cold vapor method. The results show that waters have a high level of nitrate and mercury pollution which are respectively 26.67%, (16.38 mg/l to 349.85 mg/l) and 13.33% (0.10 mg/l to 1.50 mg/l) and a low level of nitrite (0.02 mg/l to 2.63 mg/l) and lead (1 mg/l to 5mg/l). The Principal Component analysis helped to identify four groups (I-IV) of well waters: water with high degree of nitrogen pollution (NO3-) and high toxic metal and toxic metal (I: 20%); with low degree of nitrogen and toxic metal (II: 30%);water with high mineralization (III: 20%) and water rich in nitric pollutant (NO2-) (IV: 6.67%).The water pollution may be related to the low sanitation level and the improper conditions of well installation. Consumption of well waters may expose humans to health risks.