The wastewater treated by the PWTS Sanaa (Yemen), are discharged into Wadi Bani Houat to be used for irrigation of agricultural fields (cereals and "qat"). The quality of water discharged by the station is affected by neo-contamination part of untreated water diverted through bypass and also untreated effluent intake of a river that flows into the canal about 15 Km from the station. The various measurements show that the levels of contaminants studied, decrease at the exit of the station but undergo severe degradation after canal-branch river. Similarly, we noted illegal contributions at this place made of waste thrown into the canal by the surrounding population. The salinity is classified C4S2, C3S3, C4S3 and C4S4 in RICHARDS diagram, leading to poor quality water for irrigation. The ratio COD / BOD5 reaching a value of 2 after treatment and self purification of water, up to a value of 4, at a distance of 12 km along the canal before dropping to a value below 2 at the areas of retention dams located north of the study area, showing a self-purification capacity. NO2- (nitrite ions) appear downstream canal in the dams, highlighting the impact of agricultural activity on water quality. Minors cations and traces show different concentrations varying spatially and temporally along the canal during the dry and wet seasons. Overruns by FAO and Yemen standards were observed for some components such as phenol, organic micropolluant showing levels higher than standard along the canal in all seasons. The principal component analysis showed the correlation between the measured quantities and the vulnerability of sampling sites to different pollutants.
