The absolute cheapest way to make carbonated water will cost only 8 cents per gallon. You can use an inexpensive carbonator cap with a plastic bottle and a CO2 tank, or build a kegerator for this method. A soda stream will cost more, about 25 cents to 50 cents per liter, depending on level of carbonation you desire.
![Avatar](https://cdn.statically.io/img/i.pinimg.com/140x140_RS/3c/ba/52/3cba529b0c934f1a52772c7584f5dbf2.jpg)
Melanie Ems