Is water a weapon? Water is the most important resource for the formation of life, for us humans it is even more important, we don't only use water to drink, but we use it in our farmlands and in the livestock.
Water is a necessity far greater than we imagine, and all the water we consume comes from rivers, rain, and underground reservoirs. As we consume more and more water the planet starts to take a hit, let us look at some examples of water shortages in the world:

Iran:

Following decades of international sanctions Iran invested heavily in its agriculture, yet the irrigation system used is still very rudimentary and a lot of the water used on plants is wasted, as a result, Iran is facing a water shortage in many regions and it´s lakes are getting smaller by the day.

India:

India is probably one of the worst cases because people are committing suicide (in the thousands) because of crop failure, the government created thousand of miles of waterways and dams, yet they failed to achieve the objective of making water more accessible, as a result when the monsoons come too late the crops die, and farmers that go into debt find in suicide the only way out...
Another problem in India is China and Pakistan, there are huge amounts of fresh water in the Himalayas, and both Pakistan and China have territorial claims in the region.

See this awesome documentary to learn more:

Middle East:

Born in Turkey the river Euphrates and Tigris are old, and so is the history of humans in its shores. Nowadays the level of the Euphrates river is the lowest since it as been in decades, upstream the Turkey government is investing heavily in dams and the released water goes to a minimal level, creating drought in Syria and Iraq wich are already desertic areas. The bad news is Turkey is planning on building more dams in the rivers, and as a consequence, the stream of the rivers may go even lower.

Other hotspots for future water wars include Uzbekistan and Tajikistan. In the Nyle Ethiopian government plans to build a mega dam, if it decreases the levels downstream Egypt will be affected. In China, the Yellow River faces mostly pollution, yet some areas of the country in the North have serious water shortages.
More places can be added to this small list, water is becoming more and more precious as our consumption increases, Feel free to comment, upvote or resteem!!
Peace, Carlos.