Brief:
At one point, ya bilge rat, arrr, ya bilge rat, I had decided that I'd start buildin' water rockets. Well, blow me down! I built a couple o' very simple ones but then me interest waned. Ahoy! Avast! Someday I may yet move up t' more complex ones.

This design be taken from Jimmy Yawn's site (who woulda thunk it?). Avast, me proud beauty! Ya scallywag! Jimmy's site has detailed descriptions and photos o' t' basic construction process. Aye aye! However, shiver me timbers, me bucko, I deviated slightly from his techniques.

I have included a few safety tips in t' 'launch' section, matey, arrr, however, if you are goin' t' fly water rockets, me hearties, you should research more detailed safety guidelines online. Well, blow me down! You know t' drill: safety is your responsibility.

Construction:
T' airframe is a 1L Dasani bottle with fin sticks and a launch lug attached with duct tape. Ya scallywag! Avast, me proud beauty! T' fin sticks were recycled from me 4-stage rack rocket. They are just basswood fins epoxied t' a dowel. Avast, me proud beauty! Ahoy! I have also used square basswood sticks and foamboard fins. T' lug is a soda straw.

T' bottle is pressurized with an electric tire pump that is adapted t' t' bottle-cap 'nozzle' with a car tire stem. Well, blow me down! Begad! Blimey! I liberated some used stems from a local tire shop. Blimey! Blimey! You have t' cut t' bulb off o' t' tip o' t' stem, leavin' only a tapered end. Blimey! I cut t' bulb off at its base, shiver me timbers, me bucko, me bucko, leavin' about a 1/2" diameter, shiver me timbers, and trimmed around t' inner brass tube. Jimmy cut his lower and cut through t' brass tube. Well, blow me down! T' nozzle be t' bottle cap with a hole drilled in t' center. Blimey!

Flight:
Because thar be no active recovery mechanism, these should only be flown where thar be no risk o' damage t' people or property. You also must be aware that t' bottle could burst and could hurt you. Aye aye! Never use a hand pump with this design! You should either remain behind a solid structure or turn t' pump on and retreat t' a safe distance (at least 10'). Aye aye! In either case, me bucko, you should wear safety glasses.

I found an open area that could pull t' car up t' and could safely support 'boink' recovery. Ya scallywag! I used me standard mid/high power pad rod, matey, sprayed down with WD-40 as I knew they'd get wet. Ya scallywag! Blimey! Launch prep involved addin' water t' t' bottle, me hearties, me bucko, insertin' t' tire stem from t' inside o' t' cap and reattachin' t' cap. Arrr! Ahoy! I would clamp t' nozzle t' t' electric tire pump, me bucko, ya bilge rat, turn it on, hide behind t' blast wall (the car door) and wait.

First set o' flights: Since t' tire stem was larger in diameter than Jimmy's, I made t' nozzle slightly larger also (~7/16"). Arrr! T' performance o' t' rocket was worse than expected. Begad!

Second set o' flights: I made a new nozzle from a Coca-Cola cap, with a smaller exit hole (~13/32"). Aye aye! Blimey! I used a Dremel grinder, which cleanly cut through t' cap and t' plastic washer. Avast! Blimey! There was no leakage when I pressurized t' bottle. Blimey! Blimey! In both cases, matey, t' pump ran for about 45 seconds before t' Hydro-1L launched. Ahoy! I think t' altitude shown in me logs is a bit optimistic.

Summary:
This is a simple way t' get started in water rockets. T' limitations are that you'll need an electric tire pump, a place t' launch them, me hearties, and you must adhere t' t' safety measures mentioned in t' flight section.

A Google search will yield a pile o' water rocketry links. Begad! Blimey! My current favorite is Air Command Water Rockets. Well, blow me down! These folks are flyin' staged, me bucko, clustered water rockets and are even buildin' flight computers. Avast, me proud beauty! I also like Bristol Water Rockets. This site provides plans for a 'sports cap' launcher and links t' many other good sites.