Assessment of water quality index using Analytic Hierarchy Process (AHP) and GIS: a case study of a struggling Asan River

India has abundant water resources, including rivers and snow-covered mountains in the Himalayas, which can supply the country's water needs. In many areas, however, accessible water supplies are depleting due to fast population growth and the need to fulfill rising demands for irrigation, human and industrial consumption. Physico-chemical and microbiological characteristics were stuided of the Asan river water in Doon valley of Uttarakhand, India, that sampled were collected a fourteen water quality parameters at seven locations from October 2018 to March 2019. The water quality index and water quality maps was prepared in the Arc GIS software 10.7 using Inverse distance weighted (IDW) method. The sampled datasets were used to prepare a spatial water quality index map based on Analytical Hierarchy Process. Based on the results the weightage of the pH was found to the maximum (24%), BOD (17%), DO (13.7%), TDS (11.1%), EC (7.8%), TH (4.8%), CH (4.6%), MH (4.5%), WT (3.4%), AT (2.4%), Na (1.9%), K (1.7%), NO3(1.5%) and PO4 (1.3%). The result demonstrates that the water is heavily polluted towards station three caused due to the extensive anthropogenic activities. Thus, there is a need for combined government and non-government measures to enable the Asan rivers to slow their decline and return to their natural, pollutant-free state, which is crucial for the health of their environment.