I think what the author of the parent post meant was that Israel supplies Gaza with water via water pipes. The river that you're talking about is too small to be a significant source of water. The Palestinians (like Jordan, who also enjoys benefits coming from the peace accords it signed) buy water from Israel. Water is a scarce resource in that area, so it's no surprise that it has political significance.

I don't intend to single you out, and this goes for everyone posting about some far away region that's a bit more complex than what this or that source claims. I guess it's a matter of personality, but I don't feel comfortable talking about politics of far away regions, or even of my own region in some areas. I would rather talk about the simple easy stuff that I feel confident about, like this weird paragraph in the latest C++ standard. Then I wouldn't make embarrassing claims that are basically pre-chewed propaganda for the usefully ignorant foreigners. Except the Rust people. They are the devil!