Which one of the following is a reason for water wars?

The correct answer is Option (2) → Disagreement where a downstream (lower riparian) state objects to pollution, excessive irrigation or construction of dams by an upper riparian state.

" Water is another crucial resource that is relevant to global  politics. Regional variations and the increasing scarcity of freshwater in some parts of the world point to the possibility of disagreements over shared water resources as a leading source of conflicts in the 21st century. Some commentators on world politics have referred to ‘water wars’ to describe the possibility of violent conflict over this life-sustaining resource. Countries that share rivers can disagree over many things. For instance, a typical disagreement is a downstream  (lower riparian) state’s objection to pollution, excessive irrigation, or the construction of dams by an upstream (upper riparian) state, which might decrease or degrade the quality of water available to the downstream state. States have used force to protect or seize freshwater resources. Examples of violence include those between Israel, Syria, and Jordan in the 1950s and 1960s over attempts by each side to divert water from the Jordan and Yarmuk Rivers, and more recent threats between Turkey, Syria, and Iraq over the construction of dams on the Euphrates River."