Here’s a cool video from GristTV on a variety of ways to make selzter.

Below is their show notes, with more details and context:

Soda makes you burp. It can also make you sweat when you realize 80% of bottles dont get recycled. Our Queen of Pop, Umbra Fisk, shows you how to make a better bubbly beverage at home! Reduce your carbon glassprint with home-made carbonation. Watch this and join Club Soda!
Links:
DIY Soda Maker Who needs a machine? You can craft your own!
DIY Soda Guy on YouTube
SodaStream: The machine used in this video
Soda Siphons and Cartridges
Williams Sonoma
Target
Other Handy Seltzer/Soda Links:
Green Your
Carbonate Your Booze