The BBC has several maps predicting water stress for the world's future. Not surprisingly those countries hardest hit my lack of water of their populations is in the economical-political gap area around 30 degrees North.
From Senegal to the People's Republic of China people will be thirsty. The great fear is that not only climate fluctuations negatively impact water availability but the infrastructure will not be built in time to factor in growing population and possible climate changes.
The Middle East may be especially hit hard if the oil is replaced by another energy source. Without a massive money source the Middle East have nothing to soften the blow of a dwindling water supply. Already Yemen is having serious problems.
The American West is also currently having problems and the situation will likely only get worse. The artificial "Cadillac Desert" is unsustainable and unnatural cities like Las Vegas only speed up the upcoming disaster. The question of how long the Ogallala Aquifer can last will have a big impact on agriculture in the southern Great Plains.
The best way to reduce water stress is to invest in desalinization, improve internal water infrastructure, and encourage practices that reduce water waste. Without this three pronged approach many of the world's most desperate people will be at risk of lacking the most plentiful resource on Earth.