In the first episode of Voyager, Neelix and the Kazon are shown to value water extremely highly. Neelix goes hog wild over its abundance on Voyager. Jabin is impressed by a mere flask full. The Kazon-Ogla freak out over a few hundred gallons. This makes sense when they're shown to be an isolated, primitive mining village on a desert planet.
Later in the episode, the Kazon are shown to possess enormous spaceships with shields and weapons able to quickly reach the Caretaker and battle Voyager.
Voyager makes the point that the Kazon don't have transporters or replicators... but water isn't hard to make. If you have enough power you can reduce just about anything into hydrogen and oxygen and combine them to make water. If you can figure out how to maintain a warp drive, you can figure out how to make water. If there's no suitable matter where you are, fly to somewhere there is.
This is obviously a ploy by the writers to show how much more advanced Federation technology is. They wisely find better ways to demonstrate this. Anyone want to take a shot at propping it up with an in-universe explanation?
I want to get a satisfying answer, so here's some rebuttals to things going around in the comments.
Neelix: Not just the Kazon-Ogla can't seem to figure out how to make or get water, but Neelix also. He has a ship. He's jaunted all over the sector. He has a high motivation to get his hands on water to barter for Kes. He's met advanced societies who probably have the instructions for making water in basic chemistry texts.
The Kazon are on a desert planet: Space travel is casual enough they can fly to the Caretaker and form a fleet, they can fly to where there's water or the means to make it.
Water, or the means to make it, aren't abundant in the area: Hydrogen and oxygen are the first and third most abundant elements in the Universe. We're finding water everywhere we look. Just because water doesn't fall from the sky doesn't mean it's not there. There's extractable water on the Moon and Mars. There's water in rocks.
The Kazon don't know how to make water: We isolated oxygen and hydrogen in the early 1800s and were good enough at making it to fill balloons. Oxygen and hydrogen combine to make water (and a big bang). The Kazon aren't idiots like the Pakled. They can operate and repair warp capable starships and regularly interact with other species. They can pick up a chemistry textbook.
Water is not economical for trade: If someone is willing and able to pay a lot for a good, it becomes worthwhile to ship and even fight for. Spices, tea, oil, bananas, cocoanut water. Make it valuable enough and we'll conquer a third world nation to get it and ship it across the world. The Kazon-Ogla have valuable ore to trade. If they were being extorted by a single provider, they have ships to seek better deals. It doesn't have to be other Kazon either, if someone's willing to pay well above market price for an item, other traders will come.