Maybe it wasn't critical as food shortage because as you said the world is made up of mostly water and the ones that has a water problem are away from the bodies of water but no worries because they receiving a help from different countries. Often times we will see celebrities going on those dry places and they are building up a water system.
Unfortunately, that’s not the case, as we all know Africa is a huge continent all surrounded with water, and even places near the water is having trouble for 2 main reasons. One of them is the fact that water is not clean, meaning it could make you sick if you drink it and that means there would be a lot of people dying because they drank water that was bad for your health.
Second reason is that even though there are water sources near them, they can't really walk that much and come back every day, meaning there needs to be infrastructure, I mean not everywhere in EU has water too, but they have pipes bringing water to them, so Africa needs that too. This is just a common thing people don't know about.
That type of building pipelines everywhere and then keeping that pipeline clean and maintained would be a very difficult thing. I am not saying that it is impossible because most of the developed world constantly has that and there isn't a situation that should be wondered "how", they just spend a quite good amount of money for that infrastructure.
But that doesn't mean that we shouldn't really expect Africans to have the same type of deal. Doesn't mean that we will have that type of thing would cost a lot for poor nations, it is not just about building, like let's say billionaires end up paying for all the pipes, that still wouldn't be kept clean and eventually be bad after a while.