How to Build a Water Rocket

If you’ve ever dreamed about sending a rocket sky-high, you might be relieved to learn you don’t have to mess with explosives to make one fly. If you put air under pressure, like in a tire, you can use it to propel an object upwards. Add water to the mix, and your rocket will go far above the trees.

This rocket is made from simple PVC plumbing pipe and some plastic soda bottles. It’s easy to put together in an afternoon. As long as you always have an adult around, launching your rocket is safe and fun.

The plans for this rocket were developed by middle school teacher Slater Harrison. To see his detailed assembly instructions, click here.

Building a DIY Water Rocket: An Overview

Age Range: 7 and up

This rocket is propelled by the sudden release of pressurized air, so all the parts need to come together with tight seals to hold the pressure in until you’re ready to launch. PVC plumbing pipe won’t leak as long as you use the right kind of pipe cement and make sure to clean all the connections before gluing them.

A simple string-controlled trigger unlocks the pipe from the end of the bottle, releasing the pressure and sending the bottle into the sky.

Steps for Building a Water Rocket

Step 1: Cut the pipe

Using the hacksaw, cut three lengths of ½-inch PVC pipe: 2 inches, 18 inches, and 78 inches.

Step 2: Drill a hole for the valve

• Using the drill/driver fitted with a ½-inch bit, make a hole in the top of one of the PVC end caps.
• Hold the cap steady with pliers as you work, and make sure to drill straight down into a piece of scrap wood.

Step 3: Connect the valve

• Remove the small cap from the tire valve and set it aside. Slide the valve through the hole in the PVC endcap so that it sticks out the top.
• Screw the valve cap back on.
• Grab the end of the valve with pliers and pull it until it’s firmly seated in the PVC end cap.

Step 4: Glue the launcher parts together

• Line up the pipe sections and connectors in the order in which they will be assembled: solid end cap, 18-inch piece, tee, 78-inch piece, and the 2-inch piece connected to the leg of the tee.
• Using PVC pipe cleaner, clean both parts of each connection: the outside of the pipe and the inside of the fitting.
• One by one, glue the connections together with PVC pipe cement, holding the parts together for a few seconds as the cement sets.

NOTE: Always work in a well-ventilated area when working with pipe cement.

Step 5: Make a seal for the bottle

• Mark the pipe assembly 11 inches from the long open end.
• Using the flame of a birthday candle, heat the pipe evenly at this mark until it becomes soft. Then push the pipe inward to create a slight bulge.
• Hold the pipe straight until it has cooled and the bulge is no longer soft. This bulge will create a seal between the pipe and the soda bottle.

Step 6: Build a clamp for the bottle

• Using duct tape, tape nine cable ties together so that they all face in the same direction. Make sure the cable ties are parallel and their heads are lined up evenly. Tape over both sides so that no adhesive is showing.
• Slide a soda bottle over the end of the pipe and seat it against the bulge. Wrap the cable ties around the pipe so that the head of each tie faces inward and catches the lip of the bottle, holding the bottle tight to the bulge.
• Secure the cable ties in this position by tightening the hose clamp around the duct tape.

Step 7: Make a launch trigger

• Using scissors, cut the top and bottom off a 2-liter soda bottle. Flatten the bottle section without creasing it and cut a 1¼-inch hole through both sides. This spring will hold the trigger in position until you’re ready to launch.
• Drill a small hole in the side of a short scrap of 1½-inch PVC pipe. Thread the end of a 4-foot piece of string through the hole and tie a knot on it to keep it from coming out. This pipe is the trigger.
• Remove the bottle from the end of the pipe. Slide the plastic spring onto the pipe, over the cable ties, and up against the pipe clamp. Then slide the 1½-inch PVC scrap over the pipe and cable ties. Thread the string through the holes in the plastic spring. Tape the other end of the string securely to the pipe with duct tape.
• Test this trigger mechanism by pulling on the string. The PVC trigger should drop, allowing the cable ties to open up. When you let go of the string, the spring should push the trigger up and over the cable tie ends.

Step 8: Prepare for launch

• Fill a 2-liter bottle about one-third full of water and slide it onto the end of the pipe.
• Pull the string on the trigger down so that the bottle can seat against the bulge and the cable ties can catch the bottle’s lip.
• Release the string and let the trigger slide back over the cable ties to hold the bottle in place.

Step 9: Pressurize the launcher

Attach a bicycle pump to the valve coming out of the tee. Pump no more than 70 psi into the launcher.

Step 10: Launch the rocket

Make sure the launcher is pointed straight up and that there is adult supervision for every launch. Count down, pull the string, and blast off!

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