Dagnabbit, I done spoiled myself about Damaris.
Oh well, I was thinking about water and comets and Oort Clouds. Most systems should have an Oort cloud surrounding it, and our voidships enter and exit warp just inside this shell of debris. Apart from rocks, minerals, and such, it should have chunks of ice. Even the most water poor systems should still have a substantial amount of this stuff.
To supply those parched planets with ice water, all you'd need is a system ship really with an ability to haul around chunks of ice. No need to tie up a voidship to do this.
The reason why most systems don't do this is that they don't have the infrastructure to support system ships. Vaporius should have a few ice comets in the system, though it'll take quite a while to journey to and from their system's Oort Cloud. If you can set up an orbital processor/dock and have one or two system ships (armed mind you) to alternate between grabbing chunks of ice and hauling it back you'd have a decent investment into the system's economy, infrastructure, and defense. That said, is Vaporius going to be trading you anything worthwhile? Or perhaps the Ecclesiarchy will pay you to do this so that they establish "Water from the Stars" and usurp those priest-kings' authority?
(Yes, I'm thinking of doing the same whenever I get to Vaporius.)
As for exporting ice comets, it's something you'd want those NPC free captains to be doing for you. It could be, due to the vagaries of warp travel and crazy solar systems, that it'd be far easier and cheaper to haul ice water from a nearby system instead of spending weeks accelerating/decelerating to the Oort Cloud and then heading back. Even if you establish a mining post in the Oort Cloud to limit the time the ship spends there hacking away at an iceberg the size of Luna.
Just make sure to boil the water first before you drink it...