I applaud Ethiopia for being visionary....
Egypt and Ethiopia will just have to work it out....
To their credit, if water flows through a large dam for hydro-electric power use only (not massive amounts diverted for drinking water or irrigation), then the “only” water loss to the countries and people downstream is that amount lost to evaporation from the surface water now exposed in the lake behind the dam, compared to what would have been evaporated from the (much smaller) river surface already present. SO there is water lost during hydro-electric power production, but not much.
Dam failure, as one person above pointed out, is a possibility, but in today’s world, you’d hope even the Ethiopians working with Chinese money could make a simple (but large) concrete gravity dam.
Now, will the Ethiopians limit water use to power only, and where will the power be used? Cities, farms, and homes and the area?
Or to power Chinese mines and refining plants for Chinese-paid ores going back as Chinese metal to ... China!