Why we havent maps for insids water of earth?

This is a division of geologic research called remote sensing. With the advent of satellites, remote sensing is an exciting new exploratory methodology. And research has been done in exactly as you propose, looking for potential water sources. The problem with remote sensing is there is no such thing as an "underground water sensor". What the geologists have to work with is things like infra-red radiation patterns and radar frequency reflections to probe the secrets of the desert. Some very fine scientific minds are at work to try and find explanations for remote sensor readings and would love to eventually produce a water map.

The other part of your question is not related. Finding and mapping water is distinctly different from identifying its sources. To say the Nile river is a source simply because you are unaware of other ways to obtain water is highly unscientific. Much of the water may be derived from precipitation recharge, especially if the regional climate was wetter than today. Pumping water out with wells that took millenium for nature to collect can be a very short lived benefit. In the central US, much of the corn belt is underlain by the Ogallala Aquifer. For years this artesian source has been use to irrigate crops. Now it is obvious that it is being consumed much faster than it can be recharged and irrigated crops may have to exchanged for drought resistant agriculture.

<<onlly depent up on logic>>

Talking of depending upon logic, you question assumes there are no maps showing water below the surface of the Earth, and you then ask somebody to show you one. That's not in the least logical. Furthermore, there are maps showing undergound water in some cases.

As for the semi-arid areas of southern Africa being somehow connected with the source of the Nile, not only haven't you got evidence. There's also the problem of the existence of lots of evidence that your illogical conclusion is wrong. The source of a river has to be higher than the rest of the river excepting for tributary rivers, which could also be termed sources.

What do you mean exactly?

Like water stores underground?