Water in our world is available in large quantities, but it is limited in practical terms nevertheless; with a growing population, global climate change and political instability in some areas, water might become a motive for conflict, just like oil.
The lack of resources of any kind is a motor and pretext for drastic and violent change; it always was, as the history of humanity proves. It was envy against the wealthy Jews the real caue of many pogroms, and the lack of territories and useful land for agriculture was behind many European conflicts. Assyrians repeatedly assaulted Phoenician coastal towns because these were rich and had wood, a commodity that was pretty expensive for the Assyrians, living in a barren land, and there are scores of other examples.
Water is required to survive; without it, any human and most animals and plants will die pretty soon. There are exceptions like the Bactrian camel, of course, but for most living things, water is more important than anything else. The Bactrian camel can thrive for days without taking any single drop of liquid because of its particular adaptations, and that takes thousands of years to develop.
In survival courses and training programs, you learn how to get water from almost unbelievable sources and that usually suffices for one, a pair or a handful of survivors. But whenever larger groups of people, animals or plants are concerned the problem becomes much more difficult because competition becomes a factor and in most cases, the result of competing for relatively small amounts water is that every subject receives in the end less than required. Place a whole herd of whatever you like around a pond, and what most living beings waiting there will get is a muddy, stinking liquid instead of fresh water.
That seems to have been a factor for the disappearance of a vast number of species - especially amphibians - during the greatest extinction known in the history of our planet, the P-T event that wiped out almost every sinlge living entity at the end of the Permian; it dwarfed even the extinction of the dinosaurs.
At the largest possible scale in political terms, water could become in the not so distant future, a cause for serious trouble in some regions of the world. For example, the Israelis have carved for themselves an idillic niche in the Middle East by means of technology and agricultural development. However, Palestinians, Lebanese, and Syrians, mainly, nations that have far lower productivity in their own lands in terms of the plants that they grow, repeatedly accuse the Israelis of stealing their water. Whether that is true or not is one matter, but the fact that a lot of people might think that could be enough to spark yet another war in the area.
In other arid regions, similar concerns arise: in Africa and Asia, in the case of some zones in Latin America, like in Haiti or northern Brazil, poverty is associated with the lack or scarcity of this vital liquid, and hile we have oceans of it, literally, making it available to millions could mean the difference between war and peace in the years to come.
Remember: those who fight for oil are doing so for money. Those who fight for water, do so in order to stay alive, so the fight for water will always be fiercer than any other.
Glaciers like this one in Patagona will be more valuable than gold mines and oil fields.