In simple language, Egypt's interest is water. Egypt is getting all the water it needs. What is the national interest of Egypt in this negotiation or mediation by the US. It is water. So, water is not the main issue for Egypt.
In this negotiation, Egypt is not after its interest, it is after its position. Egypt's position is to have a colonial or similar control and power over Ethiopia with respect to our sovereign right to use and manage our waters, rivers and the Nile.
Ethiopia should never, never enter a binding agreement with Egypt on any future events that is natural and beyond the control of Ethiopia.
Ethiopia does not make rain and therefore can not guarantee Egypt that Ethiopia will obliged to provide her water during drought. It is up to Egypt to store water for her dry seasons. And, this is what Egypt is doing already - storing water for any future event.
So, why does Egypt pester Ethiopia so much? Egypt simply wants hegemony, control, and influence over Ethiopia's internal development for entirely different reason.
What is the real motivation of Egypt?
It is the illusion of becoming a regional power over the Horn of Africa. This will not happen. Egypt is not located on the Horn of Africa. The sole position of Egypt is to thwart the development, growth, modernization and prosperity of Ethiopia into a powerful African nation.
This is what Ethiopian need to be very clear about Ethio-Egypt dispute.
At the end of the there is nothing Egypt can do. It may use US to put pressure on Ethiopia. But at what cost? US has other more critical interests in the region that are taken care of by Ethiopia.
Why would US be the servant of Egypt and harm Ethiopia by impacting its own global interests in the Horn that are aligned with Ethiopia.
So, Ethiopian negotiators must clear like light and stand their ground. If Egypt want to swap a quid pro quo then just the Ethiopian team demanded, let Ethiopia share the management of Aswan Dam and Egypt will have the same. Ditto.
No colonial desires with Ethiopia!