Not so fast Kemosabi...Sudan might ask China for help on a White Nile dam...that's a very narrow strip of arable land on either bank of the Egyptian Nile...tinder box coming soon.
These countries could always ask Israel for help building desalination plants. If I recall correctly something like 55% of their fresh water comes from desalination, and very cost effective. Though I guess if you have a giant river running through your country you don’t think about desalination too much.
I’m sure somebody mentioned it, but there are international treaties governing the use of upstream water to protect downstream nations. In this case, protecting Egypt’s rights. Of course, having the treaty and enforcing it are two different things.