As its name would suggest, the civilization of the Indus River Valley developed mostly along the Indus River. Its development was roughly contemporary with other civilizations that relied on rivers for their growth and agricultural needs, such as those in Egypt which relied on the Nile and Mesopotamia, which developed between the Euphrates and Tigris.
The Indus Valley Civilization eventually came to encompass nearly the entire Indus River watershed, including its many tributaries, such as the Gilgit, the Shyok, the Kurram, the Chenab, and the Gomal. However, in the farthest eastern stretches of this civilization's range, it reached the upper parts of the Ganges River, part of an entirely different watershed. There is also speculation that this civilization also relied on a now-forgotten river that has since dried up. This river may have relied on glaciers that have since disappeared or become a stream that relied on seasonal monsoon rains known as the Ghaggar. However, the heart and focus of this civilization were centered almost entirely along the Indus River in what is now modern Pakistan.
It was these water sources that made civilization possible. Without predictable and reliable water sources, agriculture could not develop on a scale that supported the growth of cities and the division of labor that it required.