U have a good point but desalinating water for irrigation purpose is a costly affair. However, it can be adopted for drinking water purpose to coastal and near coastal cities. In addition recycled water from domestic wastes in big cities like chennai, bangalore can be used for agricultre purpose. Now India has paddy varieties which grow in very less water (Drought Resistant, unlike the usual one) needs to be popularized. Farmers need to be informed about the novel varieties of crops by the Governamnets which are exhisting in the market. Finally it is mainly and more of a political issue than the water issue between the farmers of two states. If given a chance, I am dammn sure that the farmers of both states can easily and ambicably solve the kaveri water problem forever.
