This video lecture from Environmental Chemistry (F.Sc. second year Chemistry) covers the factors that affect the quality of water. The quality of water is indicated by its dissolved oxygen level, usually measures in ppm or mg/L. The microorganisms inside water oxidize the biologically degradable organic content in water which is indicated by the biological oxygen demand BOD of the water. Chemical oxygen demand COD is indicative of overall oxidizable content in water which is determined by adding an oxidizing agent like dichromate from outside. Lower values of BOD and COD are indicative of pure water. Find more e-learning material and educational video lectures in Urdu at maktab.pk. These videos are free to use for promotional and commercial purpose by keeping the credits to Maktab.