Himalayan rivers are prone for drying subject to continuous drop in the glacial meltwater contribution and groundwater level. The present study is conducted in the region of West Kameng District of Arunachal Pradesh, India, covering catchment of 2 tributaries of Kameng river, viz., Tenga & Dirang-Bichom. We used stable isotopic method to trace the origin of water feeding the river as it flows from the headwater to the region of flood plain. Our observation allowed defining the Local Water line (LWL) in this region for the dry period, with the relation δD = (8.1 ± 0.3)×δ ¹⁸O + (11.6 ± 2.5‰). This equation is derived from analysis of river water sample collected during March 2021. This LWL is identical to that reconstructed using the monthly (from India, April – October 2007 ) precipitation isotope data from a station at Mawlong, Meghalaya, [δD = (8.1 ± 0.1) ×δ ¹⁸O + (11.8 ± 0.9) ‰]. The d-excess values from the two set of data are similar at 11.2± 1.8 ‰ and 11.3± 2.7‰, respectively, implying that river water is mainly derived from rainwater. Such coincidence of observation is interpreted as a common source of water for river and groundwater. Further, we compared present observation with other studies on the surface water composition in other Himalayan River systems and documented a consistent elevation pattern for stable isotopes. Our observation on spatial variability showed maximum altitude effect in the North-Western Himalaya and drop in isotope ratios with height with pronounced participation of recycled moisture in the Eastern Himalaya with presence of terrestrial biosphere.