Answered at 2:16 of the video - the claim is that the rain actually helps, as it makes the "mountain" steeper.

Yeah, but it runs along a river… which will now be salinated every time it rains.

I did a bit of Googling. It’s a desalination plant on the Dead Sea. That is the Jordan River. The stretch they are building the salt wall on is barren desert land.

Jericho is the nearest town, 18,000 people, 8” of rain a year, 2 miles from the border. They presumably get their water from that desalination plant. No towns that far south are getting their water from it. The river barely even makes it to the Dead Sea anymore. https://en.wikipedia.org/wiki/Jordan_River#Main_environmenta...

Adding a bit more salt into the famously-salty Dead Sea are the least of their problems in that part of the world. Where else would you put the salt, anyway? Putting it all into the Dead Sea would be even worse —- at least this reduces the amount that makes it back there. Putting it into any other watershed would cause vastly more harm.

It seems like a good enough solution to me. If you think about it, it wouldn’t be in Israel’s interests to inflame tensions with Jordan over this, if it were really an issue.