Human bodies are a trivial fraction of the fresh water on Earth. That makes about as much sense as stealing batteries to run the power grid.

I call shotgun on riding the sandworm.

Surprisingly this is not something explored in "Dune" among the Fremen.

What do you mean? When a Fremen dies they extract all the water from their body- Paul is given the water extracted from the Fremen he killed in a duel. And when the Fremen first encounter Paul and Jessica I think one of the first things they say is basically "so why shouldnt we just kill you for your water right now?", meaning the water in their bodies

I mean fremen killing each other for their water. There is much made of recovering their water after death, but not of inter-sietch raids to harvest the water of conquered.

That's going to be a right bloody mess there, mate!