Brief:
At one point, matey, arrr, I had decided that I'd start buildin' water rockets. Begad! I built a couple o' very simple ones but then me interest waned. Someday I may yet move up t' more complex ones.

This design be taken from Jimmy Yawn's site (who woulda thunk it?). Jimmy's site has detailed descriptions and photos o' t' basic construction process. However, I deviated slightly from his techniques.

I have included a few safety tips in t' 'launch' section, ya bilge rat, however, if you are goin' t' fly water rockets, ya bilge rat, you should research more detailed safety guidelines online. 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. Avast, me proud beauty! Begad! T' fin sticks were recycled from me 4-stage rack rocket. They are just basswood fins epoxied t' a dowel. Well, blow me down! Ahoy! I have also used square basswood sticks and foamboard fins. Ya scallywag! 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. I liberated some used stems from a local tire shop. Well, blow me down! Blimey! You have t' cut t' bulb off o' t' tip o' t' stem, leavin' only a tapered end. Avast, me proud beauty! Aye aye! I cut t' bulb off at its base, leavin' about a 1/2" diameter, me bucko, and trimmed around t' inner brass tube. Ahoy! Jimmy cut his lower and cut through t' brass tube. T' nozzle be t' bottle cap with a hole drilled in t' center. Begad!

Flight:
Because thar be no active recovery mechanism, these should only be flown where thar be no risk o' damage t' people or property. Begad! You also must be aware that t' bottle could burst and could hurt you. Begad! 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'). Ya scallywag! In either case, you should wear safety glasses.

I found an open area that could pull t' car up t' and could safely support 'boink' recovery. Ahoy! Ahoy! I used me standard mid/high power pad rod, sprayed down with WD-40 as I knew they'd get wet. Arrr! Ahoy! Launch prep involved addin' water t' t' bottle, insertin' t' tire stem from t' inside o' t' cap and reattachin' t' cap. Arrr! I would clamp t' nozzle t' t' electric tire pump, turn it on, matey, ya bilge rat, me bucko, 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, ya bilge rat, I made t' nozzle slightly larger also (~7/16"). Ahoy! T' performance o' t' rocket was worse than expected. Begad!

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

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

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