Ramaswamy R Iyer, in a rather detailed article at EPW (pdf), traces the problem that lies at the heart of the conflict to be the excessive demand by all the four states during distress years; and hence the key to the solution of the problem might as well be in reaching an understanding for water sharing during such distress years. In the process of reaching this conclusion, Prof. Iyer also summarises the history of the conflict in a rather nice manner. Take a look!