True, water has been an important factor in the Arab-Israeli conflict, and a major stumbling block in the peace negotiations - it is water, not security, which concerns the Israelis most over the return of the Golan Heights, for example. It is also true that the Litani could offer Israel some additional water. But to believe that Israel would go to war for it ignores several facts. To take water from the Litani "without significant concessions in return" would require a permanent Israeli presence in the "security zone", and probably beyond. Because of Lebanese projects upstream, there is not a great deal of water flowing in the lower Litani, especially in the summer when it is most needed.
The stress put on water supplies in Israel in the 1970s and 1980s has been met by a concerted government effort since 1986 to reallocate water away from inefficient and intensive uses (mainly agriculture) to more sustainable projects.