The water rockets we used in the summer of 2006 were one liter bottles with plastic fins made from the light corrugated sign board favored by candidates for public office and signs about zoning board meetings. I made the rockets we used, and the glue is a very sticky construction adhesive called PL Premium, it comes from a hardware store in a tube that requires a caulking gun. Other, more friendly alternatives are household GOOP (Use it outdoors, the stuff is very hydrocarbon stinky!) or 100% Silicone adhesives, which don't stick as well, but are often quite sticky enough. Because all of these have long curing periods, I like to tack things together first with low-temp hot glue.
Some of the details about my launchers are available at my personal (and embarrassingly out of date) web site, http://users.hubwest.com/gordo/waterrocket.html There is a diagram of my launch stand at http://users.hubwest.com/gordo/CO2Launcher.html There is also a link on the first page to other web sites from around the world (The sun never sets on water rocketry.) and there are many variations and possibilities.
Alternatives to the system I use incorporate #4 one-hole rubber stoppers for low pressures but a lot of fun, and either sport-caps or hose quick connect hardware. If you Google "water rockets" you will come up with more information than you can possibly use. Sadly, the Wikipedia article on the art is one of the worst I have found in that compendium.
