This study was conducted to assess the water quality of the lower Indus Basin, Pakistan. Eighty- two water samples were collected from forty-one locations of lower Indus Basin (Kashmore to Keti-Bander) during pre and post monsoon seasons. The variation pattern in the water quality has been observed in both seasons. The samples were analysed for physical quality (temperature, pH, turbidity, dissolved oxygen, total dissolved solids, salinity and conductivity), chemical quality (chloride, total alkalinity, total hardness, sulphate, potassium, sodium, iron, zinc, lead, mercury, copper, cadmium and nitrate) and biological quality (coliform bacteria). The study reveals that the concentrations of lead, mercury, and cadmium in water samples during both seasons were slightly higher than the permissible limits, whereas, all other parameters were within WHO guidelines. The higher concentration of heavy metals must be rectified by the concerned authorities in order to protect human health.