Yesterday I finished two simple water guns I made for my kids. The result was so good I decided to publish a process description for the community of makers.

I started trying out some ideas available on instructables.com but the results were poor, mainly because of the low quality of the pipe I bought at the local hardware store.

What makes this instructable unique is the construction of the piston, made of silicone. This material seems to be perfect for pistons. It is soft to fill uneven sections of the pipe and at the same time it is firm enough not to let throuh any water.

Step 1: Materials and Tools

The list of materials is quite short, but as usual it can be tricky to get really the same parts I used - unless you are from Germany and have the hardware store TOOM in the area you live in.

This is what you will need:
- 26 mm nylon pipe, 20 mm inner diameter (a PVC pipe is also fine)
- 1/2" brass peg (mine is made of brass - again, a PVC end cap would work as well)
- rubber O-ring 1/2"
- M4 bolt 20 mm long
- 2 washers
- ALU rod, 8 mm diameter
- plastic end cap
- wooden grip

You will not need any special tool apart from an electric power drill or better a press drill (see the picture with the tools)

Step 2: Cut Pipe

Cut the pipe to the desired length. I chose about 40cm. Clean the endings with a sharp knife.

Step 3: Make a Piston

You will mold the piston from a silicone paste, normally used to fill joint gaps in the bathroom.

Start by cutting a 15mm piece of the pipe. Grease the interior of the pipe thoroughly. Place it on a piece of flat plastic, which you greased as well.

Start filling the mold with silicone, slowly working your way up, trying to avoid bubles. Fill it slightly over the edge and flatten the top - as shown in the picture.

Carefully shift the mold over the edge of the piece of plastic. You do it in order to have both sides of the piston exposed to the air, thus curing faster. Put it somewhere outdoors to let it cure, it stinks...

Let it cure, at least four days. Don't be impatient or you end up with a useless piece of crap as I did in my fist attempt (see the last picture in this step).

After four days push a nice perfectly fitting silicone piston out of the mold.

Step 4: Make a Nozzle

Drill the brass peg with a 4 mm drill and screw it into the pipe end. Don't forget the o-ring.

Step 5: Drill the End Cap

Drill the plastic end cap with an 8 mm drill. Mark the center of the cap carefully before drilling.

Step 6: Attach Piston to the Rod

Drill the silicone piston with a 3 mm drill or use a spiky tool to pierce a hole through the center of the piston.

Cut the aluminium rod to the lenght of the pipe plus cca 10 cm.

Drill a 3 mm hole into the end of the rod and screw an M4 winding.

Attach the piston to the rod as shown in the picture.

Step 7: Final Assembly

Place the piston inside the tube. Oil the piston a little bit (for example with rape oil) beforehand.

Attach the end cap to the pipe.

Drill an 8 mm hole into the wooden grip. Glue it to the rod.