Many areas of the world without adequate fresh water have become habitable because

There are various possible answers to this question. Much of the Middle East has invested in seawater desalination. This is where reverse-osmosis technology is used to purify seawater. The process is energy intensive, and so it is a particularly expensive way to treat water. We must also consider that global trade has seen the mass movements of goods from one region to another. So, even if there is insufficient water for agriculture and manufacture in one region, food and goods can be shipped in from water-rich areas.