Kevin Kelly published a tutorial on making your own carbonated beverages by Alastair Ong.
In this really terrific tutorial he writes,
“I drink a lot of seltzer. So much that my fiancee says I couldn’t survive without bubbles in my water. After trying a SodaClub home soda maker (picture above right) and realizing it would cost $70 to buy a special part for it, I found a really detailed resource for building my own, simple home carbonation system for under a $100 using a CO2 tank, regulator, hose and a carbonator cap. It took ten minutes to build. I love having very good homemade soda on the cheap and not having to lug around seltzer bottles or worry about it going flat. With a scuba-like tank in the kitchen, guests always ask “What is that?!” and I really love demonstrating.”
Home Carbonation System at Cool Tools – Link.