On 5/28/2020 at 9:18 PM, jimb0 said:Additionally, carbonating a half bottle means there's a much bigger head space of compressible air to fill, which means you could potentially fit much more CO2 into the bottle that's only partially filled with liquid.
If you have the floor space and wherewithal, I recommend neither the SodaStream or the iSI (for carbonation, that is) as both are expensive in terms of ongoing costs. We converted a chest freezer (although you could also just use a refrigerator) with a tap. 10- or 20-lb tank of CO2 --> regulator --> corny keg filled with water == 5 gallons of fizzy water on tap at a time. We have two kegs for water, so that when one is emptied, we just pop the hose over (simple ball joint so it takes five seconds) and refill the other tank. It will carbonate on its own in a day or two, and there's never any kind of risk.
A 5-gallon keg full of water is heavy, though, so that's a consideration. If strength is an issue, you can use 1- or 3- gallon kegs, as well, or even just buy a carbonator cap and carb your own 2L bottles of cold water.
More expensive (but still lower TCO) would be to install a used carbonator. This whole setup is worth it for us because we drink, like, obscene amounts of fizzy water. At least 5 gallons a week or so.
I have been doing the keg method myself for a decade... last year finally got a nice tap handle plumbed in to the bar so the fizzy water line from the basement terminates into something nice looking where I make drinks rather than a cheapy looking black cobra tap. Amazing how cheap a nice tap handle was on ebay... something like $30. It helps that the "bar" is actually an Ikea press-board bookcase that I had zero compunctions about drilling through...
I've also found that delivery of fizzy water is much smoother when I have 2 kegs in series hooked up to the tap line... service keg out-port hooked to tap line, service keg gas port connected to a jumper attached to aux keg's out line... Also makes it much less likely that I'll run out of fizzy water...
With some careful shopping and good luck, you could probably get a reg/keg setup going for less than the cost of a SodaStream thingy... presuming you rent your CO2 tank... But that would require diving down the homebrewing rabbit hole in a very serious way, as this equipment and info about it is not commonplace... then you'd have to figure out where your local welding shop is and make friends with them too, to keep you in gas... and that opens the door to thoughts of playing with liquid nitrogen and dry ice too (since the welding shop will also sell them)... which may be more temptation than most people are ready to resist...