I’m not sure about that “totally solvable to mutual satisfaction.” Even if it there is enough water now and they can reach agreement on sharing the water’s advantages (which means Egypt has to give up something), looking at population growth (about 2% a year for Egypt (https://en.wikipedia.org/wiki/Demographics_of_Egypt), 2.9% for Ethiopia (https://en.wikipedia.org/wiki/Demographics_of_Ethiopia), that can change rapidly.
If those growth rates continue the per capita amount of Nile water will halve in 25-30 years.
Is per-capita water a relevant metric? I doubt human consumption is a significant portion of water demand - I mean, doesn't farming typically use the vast
majority?