For exams, it's most important to remember the river and the start/end points for the first two or three waterways:
\[\begin{array}{rl} \bullet & \text{NW-1: Ganga River (Prayagraj-Haldia)} \\ \bullet & \text{NW-2: Brahmaputra River (Sadiya-Dhubri)} \\ \bullet & \text{NW-3: West Coast Canal (Kollam-Kottapuram)} \\ \end{array}\]