Sparkling water is one of my favorite drinks; it’s refreshing, it makes you burp, and it can be used for cocktails and cooking. I looked into getting a Sodastream system but I really don’t like the business model. It’s basically the disposable razor blade model where the upfront cost is low but the lifetime cost is high, and the profit is made on the refills.
I knew about the Carbonater bottle cap from my dad’s homebrewing setup. He uses it to keep beer that has been kegged and force-carbonated fresh for transport after it’s poured. Using this cap with a CO2 tank, a regulator, and a gas line with a ball-lock valve, you can make your own carbonated beverages for much cheaper than with a sodastream. The upfront cost is a little higher, but you can also use this setup with a couple other parts for a kegerator.