Not to mention that in some places, carbonated water at the supermarket costs way more than USD0.8 per bottle, and that you don't need to pay 17USD for a refill

Not to mention that in some places, carbonated water at the supermarket costs way more than USD0.8 per bottle, and that you don't need to pay 17USD for a refill of gas, at least in Europe you pay for the gas bottle, but the refills are about half that price. We've had a sodastream for over 4 years now, and have actually saved a big chunk of change on it...