When I wrote up our office experience with the SodaStream Genesis, some readers asked just how much money you can save using the device. The answer? It's actually possible to buy ready-made soft drink about the same, so the value equation depends on your preferences.
A standard container of SodaStream flavouring (such as the cola or ginger beer flavours we tested) costs $6.95 and produces 12 litres of drink. That makes the per-litre drink cost 58 cents. But that doesn't include the cost of buying the equipment, or the cost of occasionally having the gas cylinder refilled. Commenters estimated gas cost per litre at close to 30 cents.
Can you buy soft drink for 58 cents a litre? Not quite. A 1.5 litre bottle of Home Brand cola costs $0.95; 2 litres of Coles Smart Buy Cola costs $1.28. That works out out at roughly 64 cents a litre either way. Given that the SodaStream product tastes like generic cola, it's a fair comparison. And once you factor in gas costs (let alone setup), you are paying rather more than the very cheapest drinks (unless you just want soda water).
That doesn't mean it's necessarily a bad investment. You might prefer being able to customise your own flavours and use cheaper options such as cordial or apple juice; you might prefer the SodaStream flavourings to their pricier commercial equivalents; you might appreciate not having a car boot full of fizzy water; you might not want to contribute to all those trucks delivering the bottles to the supermarket. As with most shopping decisions, there's no single universal answer: research and identifying your own needs are the key.