I drink at least a liter of sparkling water every day. It's so fresh, so good with food, so... fizzy. But I quit buying it a long time ago, in favor of a SodaStream seltzer maker. SodaStreams can get a little expensive, though, and the CO2 canisters aren't very large. If you are the handy type, and are willing to handle some details measured in psi, you can build your very own under-sink carbonator. Here's how, courtesy of The Etsy Blog.
An Etsy blog reader shared a very detailed and thorough step-by-step for making a home carbonation system — complete with an equipment list and step-by-step photos.
It doesn't look terribly challenging, thanks to these great instructions. The benefit of this system, too, as compared to a SodaStream, is that everything sits tucked away under the sink instead of out on the countertop. Also, you can use a much larger CO2 tank; the writer says it lasts him all year, as opposed to the two or three weeks a SodaStream tank lasts in my household.