a 16oz water bottle won't give you any noticeable results. I am currently using a 20oz gatorade bottle, and that barely gives me any bubbles.
In a perfect world, you should use a 2 Liter coke or sprite or whatever bottle, and fill it with 6 cups of water, 3/4 cups of sugar, and a teaspoon or two of yeast. BUT the trick is sealing the bottle completely. Here is a quick step-by-step on how to make one.
1. Get airline tubing (3/8" i think) and make sure that it will reach the bottom of your tank and have plenty of slack for moving the bottle around.
2. Get a 2L bottle of coke.
3. Host a party and drink all of the coke :P
4. Drill a hole in the top of the coke bottle and insert the airline tubing through so there is about 1/2" of tubing inside the cap.
5. Cover the top of the cap with hot glue. I don't know exactly how far you should glue it, I guess, just go crazy to make sure that air won't escape.
6. If you want, put aquarium-safe glue on the inside. I just used a tiny bit of hot glue on the inside, but its probably not too great for my fish.
7. Fill up the 2L bottle with 6 cups of water and 3/4 of a cup to 1 cup of sugar. Let it sit like this (but with the cap on!) until the sugar completely dissolves into the water (basically just let it sit overnight.)
8. Put 2 teaspoons of yeast into the bottle, and screw the cap back on. Gently shake and swirl the bottle around for a little while, and after a few hours, the mixture should be readily producing CO2.
9. Call up a friend and have him give you a pat on the back for doing something really cool.