How to Build a Water Rocket

For many years, rockets have been fascinating and inspiring people all over the world. Kids and adults alike have celebrated this conquering of nature and now you can bring the wonder into your own backyard. While many model rockets use explosives or other chemicals, these instructions can provide the means to a safe rocket that you’ll want to launch over and over again. This water-powered rocket can offer an educational experience for a kid, or just a fun way to spend a weekend.

A Word About Safety
• Launch the rocket outdoors at least 100 feet from any surroundings.
• Make sure that everyone is aware when the rocket is being launched.
• Do not compress the rocket more than instructed.
• Ensure that the rocket is launched at a vertical angle to avoid an unintended flight path.
• Attach a parachute to the rocket to ensure that it comes back down safely.

¼ inch air compressor fitting
¼-3/8 inch brass adaptor
3/8 brass valve
3/8ths nipple
3/8ths – ½ inch galvanized adaptor
½ inch slip to inside thread PVC coupling
½ inch slip to outside thread PVC coupling
½ inch PVC “T”
½ Inch PVC elbow
½ inch PVC plug
½ inside thread to ¾ slip coupling
½ inch PVC valve
1 ½ inch PVC coupling
½ inch PVC coupling
½ inch PVC pipe -5-foot length
PVC Cement
Hacksaw (fine tooth blade)
Long Zipties
Sharp Knife
Teflon Tape
Hose Clamp
Tape Measure
Sharpie

Cut 5-foot length of PVC pipe into:
• 1 24-inch length
• 2 3-inch lengths
• 2 10-inch length
Remove plastic burr after all cuts to improve seals

Glue T-junction to end of 24-inch length of PVC
Using glue cap, apply glue to the outside of the 24” segment, and then quickly insert it into the T-Junction
(Follow this procedure for all “glue-in” joints)

Glue 10-inch lengths to open slots in the T-junction

Glue ½ coupling to one end of assembly, then glue 1/2 “ end cap to open end of coupling.

Attach ½ glue-in to screw-in coupling to opposite side 10” length (the one that's not capped), then apply Teflon tape to outside of the ½” to 3/8” adapter. (At least 3 layers) and  screw ½” to 3/8” adapter into coupling on end of assembly.

Now screw 3/8” nipple into adapter on end of assembly, and attack the 3/8” brass valve. 

From here, screw in the 3/8" to 1/4" adapter to the end of the brass valve. Attach the 1/4" air compressor fitting to this.

Note: you must apply the 3 layers of Teflon tape to ALL screw in connections for them to be of sufficient strength. 

Glue PVC elbow to open end of 24” length. (Must be pointed as close to vertical as possible).

Insert  and glue one of the 3” segments (from step 1) into the elbow, then add valve to the top of the 3" segment.

Add the other 3” piece to top of valve, and connect the ½” to ¾” thread adapter to top of assembly (Screw side up). 

Now, screw on the 3/4" screw-in to glue-in adapter to the top.

Now, slide the 1 1/2" PVC coupling over the vertical pipe down to the valve (it will fit loosely and rest there).

Using hose clap, clamp on a ring of zipties around vertical pipe such that latching mechanisms are pointed inward just above top adapter. The ziptie latching mechanisms should form a ridge that will hold the bottle down when the 1 ½” coupling is slid up to cover their lengths.

The Launcher is now complete, see following steps for rocket.

Roll of Duct Tape
Roll of Strapping Tape
At least 1x #17 O-Ring
Primer (optional)
3x 2-Liter Bottles (brand doesn’t matter)
1x Tube of PL Polyurethane construction adhesive
At least 2 sheets of Cardstock
At least 1 square foot of Cardboard
Garbage Bag (for parachute)
String (to attach parachute)

Select 2-liter bottle that is in best condition – this will be the "Engine Bottle", and it is important to keep it away from sharp objects.

Remove plastic cap ring and insert O-Ring into place just below threads on top of bottle. Set bottle aside, and try not to damage it in any way.

Select another bottle. This will become the fin ring. Excise a 3 ½” segment of the bottle.

It is helpful to use a doorjamb to make clean marks. By bracing the bottle against the doorjamb, you can rotate the bottle without it moving. By holding a sharpie steady, you can make a perfect circle around the bottle, giving you a straight line to cut.

Mark lines for fins at 90° intervals around the outside of the excised ring. It is also helpful to use a doorjamb for this, as you can brace the bottle vertically and use the jamb as a guide to draw straight lines.

Mount the ring around the top of the motor bottle. Seal in place with strapping tape.

Cement ring in place using PL Cement. Apply line of cement to inside joint and smooth with finger. It is Critical that you do not substitute any other form of cement for the PL Cement - other cements will degrade the plastic of the bottle.

Cut fins from cardboard. Fin design is at your discretion; the design we used provides a decent base for the rocket to sit on. If you want to get creative with the fins, do so!

Tape the edges of the fins that will not be attached to the rocket. This will improve airflow and protect them if you chose to paint your rocket. The side that will be glued to the rocket is left un-taped to make it attach better.

Now you will attach the fins to rocket fin ring. Using PL Cement, attach fins to ring on marked lines. For extra stability, put a line of PL cement down the side of the fins, and you can smooth this out with  your finger.

It is important to note that the bottle opening will be the exhaust for the rocket and will be pointed down during launch. Brace the fins as necessary to allow the cement to set up. The cement will take up to 24 hours to set up. It is important that you do not handle the rocket during this time.

Now, you will assemble the nose of the rocket. This part of the rocket is far more tolerant of errors than the engine section, so feel free to get creative with design.

Select a third bottle, and using knife split the bottle in half along it’s lateral axis.

Attach top half of bottle to the top of the motor section, and seal in place with strapping tape.

Fashion a nosecone out  of cardstock, large enough to enclose a garbage bag.

Using some form of string, attach a garbage bag to the top of the rocket. Pack this garbage bag under the nosecone.

Rocket Complete - This is what ours looks like when finished.