It doesn't have to be "much" cheaper, though. That's the entire point: if they can undercut it by even 5%, it's worth it. Plus, you can then fill up the Progresses and ATVs with more useful stuff.Sarevok wrote:But who would buy the water ? The ISS requires only 15000 pounds a year. If you are turning the water into propellant or fuel very few satellites ever go beyond LEO. At the prices they suggest it is not really much cheaper than launching it from Earth.
The launch rate of ISS supply ships is constrained by more than just money, but also things like launch windows, vehicle availability etc.
Ordering some water from an on-orbit supplier is overall much simpler, from a logistics as well as monetary standpoint.