This article appeared in Make: Vol 71. Subscribe now for more tips, projects, and skill builders.

When invading Germanic tribes deposed the last Roman emperor, Romulus Augustus, in 476 AD, Western Europe fell into a period of intellectual stagnation. The next five centuries were, for European-based science and technology, a very dark age. But the light of science was not snuffed out; instead, it found new places to shine, namely, China, India, and the Arab empires.

The 8th century saw the city of Baghdad quickly grow from a small settlement on the banks of Tigris to a military, commercial, and scientific powerhouse. In fact, Baghdad soon became one of the world’s most important centers for education, culture, and the exploration of science.

The rulers of Baghdad were the caliphs of the Abbasid dynasty (750–1258), and some of them had a deep and abiding interest in technology. They invested a substantial amount in scientific explorations of many kinds.

The best remembered Arabic engineer of that time was Ismail al-Jazari, who was born sometime in the mid-12th century and died in 1206. He is known primarily through his landmark book, The Book of Knowledge of Ingenious Mechanical Devices. Published just before his death, its pages are filled with a plethora of descriptions of ingenious mechanical devices, along with Make: magazine-like instructions showing how to construct them. Included there are how-to advice and illustrations describing about 100 robotic automata, water fountains, water pumps, and clocks. Like Leonardo da Vinci, who lived 300 years after him, al-Jazari was a polymath adept at many things, and like da Vinci, he is widely remembered for sketches and notebooks of ahead-of-his-time ideas and gadgets.

Figure A

Modern biographers credit al-Jazari with inventing, refining, or at least anticipating many important technologies. Examples include sandcasting, valve seats, a windproof lamp, plywood, and an automated water flow regulator.

Figure B

Historians place al-Jazari in the front rank of scientists and engineers from his era. His books are so detailed that many of his devices have been reconstructed by modern makers working from the drawings they contain. Some, like his famous Elephant Clock (Figure A), are so remarkable that several reproductions have been made and currently amaze visitors in museums and other public areas around the world (Figure B).

Figure C

In this issue of Remaking History, we create an al-Jazari-inspired water clock. Like the original, our Elephant Clock has two interesting features that al-Jazari either invented or improved upon (Figure C). The first feature is an automatic float valve that keeps the water level in a tank constant, thus allowing a constant flow rate of water out of the tank. Normally, the rate of water leaving a vessel through a hole in the vessel’s side or bottom slows down as the water level in the tank drops. This phenomenon, known as Torricelli’s Law, is a big problem for water clocks because they indicate the passage of time by showing the difference in the height of water levels from one timing mark to another. Such nonlinear flows make measuring elapsed time very complicated. But with al-Jazari’s automatic valve, the water flow in or out of the measuring tank is always constant.

The second interesting feature is the Elephant Clock’s ability to adjust the rate of flow out of the tank. In al-Jazari’s time, the length of an hour was determined by dividing the time between sunup and sundown into 12 equal parts. So, the length of an hour varied greatly by the time of year. Al-Jazari’s Elephant Clock had an adjustable flow spout that could be easily adjusted to run faster or slower by rotating the curved spout to change the clock’s pressure head (the height of the water in the tank above the orifice from which it flows out).

Make Your Al-Jazari-Inspired Water Clock



  • PVC pipe, white, 3″ diameter, 20″ long
  • PVC pipe, clear: 4″ diameter, 12″ long, and
  • 3″ diameter, 8″ long
  • PVC couplings, white, smooth to smooth:
  • 3″ diameter (1) and 4″ diameter (1)
  • PVC reducer couplings, white, 4″-to-3″ (2)

Adjustable flow spout:

  • Rubber stopper, #0 size
  • Copper tubing, ¼” O.D., 3½” long

Automatic flow control valve:

  • PVC pipe, white, ½” diameter, 4″ long
  • Balsa wood circle, 2¾” diameter, 1″ thick You can easily cut this from a square piece using a coping saw.
  • Foam rubber circle, 2¾” diameter foam rubber circle, ¼” thick I used scissors to cut up an old mouse pad.
  • DWV pipe fittings, inset test cap, 3″ diameter (2) These are available in the plumbing section of all big box and most hardware stores.


  • Rubber mallet
  • Electric drill and drill bits
  • Hammer
  • Hot glue gun and waterproof hot glue
  • Epoxy filler such as J-B Weld WaterWeld Epoxy Putty Stick
  • PVC primer and cement
  • Coping saw or bandsaw
  • Copper tube bender (optional) helpful but not 100% necessary

1. Make the adjustable flow spout

1a. Drill a ¼” hole in the center of the #0 rubber stopper.

Figure D

1b. Use the hammer to crimp one end of the copper tube, leaving only a very small orifice for the water to exit. Now, bend the copper tube into the shape shown in Figure D using a tube bender.

TIP: If you don’t have a tube bender, you can fill the copper tube with salt, plug the ends, and form the tube by carefully bending it with your hands.

Figure E

1c. Insert the bent tube into the rubber stopper hole (Figure E).

2. Make the automatic flow control valve

2a. Hot-glue the foam rubber circle to the balsa wood disc.

TIP: You can use a few ½”-long nails to attach the foam rubber to the wood if you have trouble gluing it.

Figure F

2b. Fill one side of a DWV test cap with mixed epoxy putty and allow it to dry (Figure F). Drill a 7/8″-diameter hole in the center of the cap. Insert the ½” diameter (ID) pipe into the hole, extending one end 2¼” past the bottom. Square the pipe to the bottom of the test cap and hot-glue the pipe into place.

Figure G

2c. Use the PVC primer and cement to attach the test cap/pipe assembly to the inside of one of the 4″-to-3″ PVC reducing fittings. Make sure the 2¼”-long end of the pipe is on the side with the 3″ opening (Figure G). Add a bead of hot glue to the connection to ensure it is watertight.

2d. Drill a 9/16″ hole for the stopper on the side of the 3″-diameter clear PVC pipe, 2¼” from the bottom. Drill a ¼” vent hole in the same pipe, 2½” from the top.

Figure H

2e. Use the PVC primer and cement to attach the remaining test cap to the inside of the 3″ white PVC smooth coupling. Add a bead of hot glue to the connection so it’s watertight. Figure H shows how the float valve will look in action.

3. Assemble the water clock

Figure I

3a. Assemble the water clock by connecting the PVC fittings, wood float, and adjustable spout
as shown in the assembly diagram (Figure I).

Use the rubber mallet to seat the fittings onto the pipe. Note that only two joints are cemented together using the PVC primer and cement. The others must be able to be opened for troubleshooting and cleaning.

3b. Optional: You can add some color to your project by using dye to stain the white PVC pipe and fittings. For tips, see Sean Michael Ragan’s tutorial.

Using Your Al-Jazari Water Clock

To set up the water clock, slowly fill the 4″-diameter water reservoir pipe with water. As the top tank fills, water will flow into the second tank. As it does, the float will rise with the water. When the foam rubber contacts the bottom of the ½” pipe, the rubber seals off the pipe, preventing additional water from entering the second tank. But, as water exits the second tank via the spout, the level falls, unsealing the tube, and water flows again. This process repeats indefinitely as long as there is water in the top tank.

To gauge the passage of time, mark the water at the beginning by making a mark on the 4″ clear PVC with a dry erase marker. Then use the marker to mark whatever time intervals you’re interested in on the side of the top tank.

By rotating the spout up or down, you can control the rate at which the water exits and therefore the amount of time between marks. When the spout is up, water flow is decreased. When the spout is down, the pressure head is larger and the water flow increases.