TN has only one major river - Cauvery. Karnataka has many Krishna, Godavari besides Cauvery. Water cannot be shared based upon from which state does it originate or what the catchment area %age is, but based upon needs. No award can be perfect for Karnataka if it has to share water with any of the states whether its AP , TN or Goa.
If the Union Govt cannot solve this problem, then we should wonder why the hell we are living in this Union.
