Is it difficult to make use of ocean waters?

We hear of scarcity in potable waters and waters for agriculture. We observe governments creating conflicts for river waters (example Nile water).  We listen that water is scarce and fixed resource and that the potential world war of the future would be for water. Is it so difficult to make use of ocean waters for drinking, agriculture, industrial, power and other purpose?

It is true that ocean or sea waters are currently used for navigational purposes and sea food extraction but not or rarely heard used for drinking and agricultural irrigation purposes. Why? We have reached to a civilization where the vast world shrunk to village. We hear wonderful technologies invented frequently. Why innovators and scientists become unable to invent technologies that purify the salty nature and other elements of the ocean waters to be used for human needs?

We know from our elementary school that two-third of our globe is covered by water. Apart that there is underground water although the size may not be known. Why are people afraid of shortage of water and why countries they intend creating conflicts with other countries for the sake of water? Is it not technology lagging behind?  Of course, one main reason for technology lagging behind is that water is not commoditized yet and does not give technologists incentives. In my opinion, water need to be commoditized so that water treatment technologies can be invented and water conservation and economic utilization can be addressed