The water quality Index of water has the highest degree of usage among the other water quality Indices, and it has been used for classification quality — Index of watershed area of latiyan dam . Determining the condition of water in Jajrood River and Latiyan Dam as one of the most important drinking water resources of Tehran and regarding capital’s population increase is of great importance.
In this research , according to the result of the measurements carried out by Tehran’s water and sewage company and by the research center of Water & Energy, the quality classification of Jajrood River’s and the drainage of latiyan Dam’s water have been done separately.
According to the result of the obtained quality Index , the quality of water near some populated ares is low of microbes and bacteria's and suspended particles entering the water and making it unclear . the quality of water in the river is beter in autumn than in summer.
Also, the results obtained from this Quality Index have been compared and analysed with the result of other method introduced in this paper. The comparison shows nearly similar result in quality classification of the River width.
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