I'm taking a break from water rockets while I work on the pond but still keeping an eye on the water rocket message board. Someone posted a link to rockets using flour instead of water. Once you take a look at the pictures you'll see why. They won't be setting altitude records but the cool blast-off effect is worth it.
The site is in Thai but once you make it to the photos it is pretty obvious. Like the launching water rockets from underwater page. Here's their homepage.