I can't tell if you're joking, but photosynthesis rearranges carbon dioxide and water into sugars, releasing some of the oxygen from the water molecules.

And when you burn the algae sourced synthetic kerosene and algae sourced O2 in your rocket engine (or whatever you're doing with it) you'll run out of water. And its dumb to ship unprocessed water up into space if you can use cheap earth based refineries to ship the same weight of highly refined fuel. Keep those heavy refineries at the bottom of the gravity well unless you have a really good reason to hoist them up.

So that was the origin of my idea that this isn't going to scale in space "in general". I'm told Europa has a lot of water, other than the whole lack of sunlight thing, I could see Europa as the "fuel tank of the solar system" in the future. Maybe it could be economically viable to mine comets and turn them into fuel while they're near the sun? Or mine icy asteroids?

I think you're going to overall have more trouble finding water in space than energy.