I'm lacking a bit of context. Your comment implies that 7 years is a long time to fill a reservoir. I can't find, either in your comment or in the article, me

I'm lacking a bit of context. Your comment implies that 7 years is a long time to fill a reservoir. I can't find, either in your comment or in the article, mention of whether that time is long due to the amount of water needed (the bathtub is big), or whether that timeline is deliberately long to avoid impacting downstream usage (the bathtub faucet is at a trickle). From the article, the Nile river is estimated to carry 84 billion cubic meters per year, so the reservoir holds roughly one Nile-year of water. Filling over 7 years means that the downstream flow would be reduced by ~1/7 during that time period.