I've heard a lot of talking heads worrying about a future war over natural resources, either oil or water. While it's an interesting idea, I don't believe it's likely, for one simple reason: it's never happened before. There have been shortages of strategic materials before, and past oil, water and even food crises. But there has never been a full-blown war between two countries over natural resources, fought out of dire necessity. Well, not in 4,500 years. The last (and only recorded) formal war fought over water was in 2500 B.C.
One could argue that Saddam Hussein invaded Kuwait for its oil. But Iraq didn't need Kuwait's oil: they were, and are, an oil exporting country. Similarly, some have argued that the United States and her allies fought the two Gulf Wars over oil, but even if that is true, Iraq and Kuwait represent a small portion of the U.S.'s oil imports (less than 10% combined), so I don't see how that implies a dire necessity.
Iraq and Syria have had serious water disputes with Turkey, which has dammed several rivers that flow through the three countries (including the Euphrates). But they have not gone to war over the issue. Similarly, Israel's neighbours claim that it is taking more than its share of the water resources of the region. But Jordan and Syria have not attacked Israel because of it.
Resource shortages- especially of food- have provoked riots, rebellions and revolutions. But they have never provoked international wars. Why? Because poor countries do not attack rich ones. The weak do not attack the strong. If one country has a resource which another country wants, the latter country can simply purchase the resource (sometimes at an inflated price). Rarely will a supplier country refuse to sell a resource at any price, unless they don't have enough for themselves. In which case, attacking that country will do little good, as the defenders will fight desperately to keep what they have, and spoil it rather than surrender it to their enemy.
Wars are not fought because of necessity. They are fought because of greed. They are fought by the strong against the weak, and by the weak in defense against the strong. Sometimes they are fought for ideological reasons, but usually ideology is an excuse for ambition. The Arab conquests of the 6th and 7th Centuries were not really about spreading Islam, they were about plundering their neighbours. Likewise the Spanish conquests in Latin America were supposedly for 'God, gold and glory', but God and glory had nothing to do with it. It was gold, and gold alone, which fired the conquistador's hearts.
There is no question that there will be oil shortages in this century. That resource is dying out. Fresh water, likewise, is becoming scarce in some countries. But will there be wars as a result? History says that it is unlikely.