Eco-friendlier: Soda water in bottle or cartridges and machine?

After realizing that I consume 2-3 bottles of soda water a day (sometimes natural sparkling mineral water sometimes just carbonated) I decided to invest in a carbonated water maker like this. Cost about $50 and the CO2 cartridges come out to about 40 cents apiece (1L of carbonated water usually costs me about $1).

The system isn’t perfect (occasional leaks, fizz peters out after a day), and I’m not saving THAT much money, but what I really want to know is – is this, as I’d assumed, better for the environment? I know a truck doesn’t have to transport water, so that’s a plus, but is less energy going into making those cartridges versus plastic bottles? Or to recycle either?

Thanks in advance for any insight! I wasn’t sure if there would be a definite factual answer for this, or if this counts as food, so I hope I have the right category.

It’s probably a wash. I’m guessing it takes a lot more energy to produce a 12 or 16 gram CO2 cartridge than a 1-L plastic bottle. But it probably costs a lot less to transport a pack of 24 cartridges than 24 L of water, so that might even out. Both are easily recyclable, although you save more energy recycling a ton of steel than a ton of plastic.
In any case, the difference (if any) is likely very small compared to the amount of energy you use driving to the supermarket once. So if you can eliminate even one trip to the store by stocking up on CO2 cartridges (120 cartridges will easily fit in your pantry, while 120 water bottles take up a lot of space), I’d say they’d be the “green” choice.