Alex had nearly the identical problem. He never mentioned salt but definitely described it as "like drinking out of a stagnant fish pond".

The good news is that it didn't last very long (a month maybe??) and he got by with apple juice. It was the one that didn't burn his mouth to my great surprise (I thought it would for sure) and on chemo days, my first job while Alex was checking in, was a race to the fridge to purloin 6 packs of apple juice for the day.

I think that you might need to move on to flavoured things. Alex couldn't do milk (thick and choked him), orange (burned) tomato (burned), pineapple (burned AND tasted foul). We tried flat soft drinks but I don't recall the outcome. The fact that I can't, suggests that it wasn't terribly successful.

He used flat soda water for swilling/teeth cleaning and I don't think he had a problem with the taste of that but he didn't drink it either.

Just keep trying, I hope you find something sooner rather than later