Hindu-Kush Himalayan region maintains the sustainable livelihood of about one-fourth of the world’s population. They are the largest storage house of fresh water in the world. The presence of glaciers all along its arc-shaped areal extension makes it the third pole in the world, after Antarctica and the Arctic. This chapter tries to give a detailed account of the significance of mountains in the hydrological system of the world, highland-lowland interface, sources of water in the Himalayas, major river systems, i.e., Indus, Ganga, and Brahmaputra, and natural and anthropogenic influences on these water resources. Various sources of water in the Himalaya such as glaciers, springs, rivers, dams and reservoirs, and groundwater aquifers not only fulfills the requirements of hilly Himalayan terrain but also renew the soil fertility, boost agricultural yield, provide water for drinking and industrial purposes, facilitate electricity generation through the construction of dams for the people residing in the lower areas. The Himalayan region also facilitates a tourist destination for people all around the world who wish to enjoy snowfall and natural beauty. The hot springs prove medically helpful in curing skin-related diseases and mental calmness. Analyzing the water resources in the Himalayan is crucial as climate change is leading to an increased rate of melting of the glaciers, leading to a decrease in the quantity of water stored in this high region for the perennial supply of water to meet the demands of one of the densely populated regions of the world. It is in this backdrop; that the present chapter attempts to give an account of the hydrological resources present in the Himalayas.