This map is just an approach to the reality. Some countries - for example Spain, Saudi-Arabia and Australia - have insufficient water reserves, but they are rich enough to buy foreign water. Others, like Russia, have definetively regional water problems: e.g. the area of the Aral lake is devastating cause of the cotton cultivation - and even in the US (in the south and in the middle-west) there are similar areas.

And a small local example: Some municipalities in the mountains of the Eifel (Germany) which are rich of water have problems because they are selling it to the Netherlands (which have as well a water problem but are rich enough to by it in the neighbourhood)