I gave it a month before posting. But I am so glad I finally bought this gizmo. Had been thinking about it for, literally, years. I am incurably addicted to fizzy water so I'd been buying either expensive imported fizzy water or big bottles of club soda for my fix. I always felt guilty and stupid about the waste of disposable bottles, the unconscionable transportation cost and the fact that I should be drinking our own, homegrown beautiful well water.
So I bought the Sodastream water carbonator. It's a unit, about the size of an average coffeemaker (a little taller). You put a CO2 cartridge into the back - which should carbonate about 60 litres of water - fill the two supplied re-usable bottles with cold water, attach them to the unit and in about a minute you have a bottle of fizzy water. You control the amount of fizz you like - I like mine pretty bubbly. I LOVE this machine.
It's not free. The unit cost about $100 (ish) in Canada and it comes with one carbonator cartridge and two bottles. I bought two additional bottles (about $18) and just yesterday two additional carbonator cartridges. The cartridges cost me $34 each, but when I return them empty and pick up a full one, it will only be about $16 for each one. There's a deposit that you only pay once.
I love that I'm drinking my own water, it has no added sodium or anything that isn't already in the water and I don't have to throw away or recycle zillions of empties. It was a great investment and will save a bit of money in the long run.
Just wanted to share in case anyone else is considering this unit.