When we were shopping around for a Pack to join, the Tiger den of one of the Packs we visited launched water bottles. I chatted with the den leader and received some verbal instructions, and supplies were picked up within the next week. We didn't actually build it until a month or so later. And we got one of the fittings wrong so now we're tinkering with it until we get it so it's as easy to utilize as the one we witnessed.
Meanwhile, we found a Pack that is very close by and has a great vibe to it. The Cubmaster had built a different water bottle launcher than ours, and he had the Pack out to his house to build rocket bottles and roast marshmallows.