Groundwater Level Measurement Probe for Low Resource Settings

Introduction

We received a request from Oxfam to develop a simple way with which school children in Afghanistan could monitor groundwater levels in nearby wells. This page has been translated into Dari by Dr. Amir Haidari and the translation can be found here. Costs should be low and one should be able to make it with locally available materials. We will start with a design that should work in most places but there is a lot of room for alternatives and improvisations. I used a cheap alarm to make a sound but a simple toy may work just as fine.

The traditional simple way to measure groundwater levels in a well is with a little bell, basically a metal pipe that is open on one end and closed at the other, on a measuring tape (see picture). When the bell is plunged into the water, it makes a popping noise, as shown in the video.

It takes some practice to use. An electronic version is easier to use and more fun to make.

Note that for most parts it will not be difficult to find alternatives, which is why some items are followed by a functional description in brackets.

Materials (see Photo A)

1. Cheap alarm
   (an electronic device that makes a sound when a switch is closed, think toys, buzzers, ...)
2. Empty tube for effervescent tablets
   (any watertight housing that can hold the circuit and battery and fits in the well)
3. Stiff copper wire
4. Solder, wire
5. Hot glue
   (any glue or kit that can make a small hole watertight)
6. String, tie wraps, duct tape
   (this serves to tie the device to the measuring tape)
7. Surveying measuring tape
   (one could make one oneself by marking distances on a rope)

Tools (see Photo B)

1. Soldering iron (can be much simpler than the one shown here)
2. Hot glue gun
3. Hobby knife
4. Safety glasses

It is important to carefully select a gadget that generates sound when a switch is closed or a button pushed. Markets, stores with cheap "stuff", hardware stores, second hand automotive parts, these may all be a good source. I checked a cheap toy, a birthday card that played music when opened, and a smoke alarm but ended up with a window alarm I found in a hardware store for two Euros but can probably be found for much less. The following criteria should be taken in consideration:

• The switch or button should not turn on the complete circuit. In that case, all the energy will flow through the switch. In our case, the switch is a connection through water, which conducts reasonably well but has a much higher resistance than a closed switch or pushed button. The birthday card had a switch like that and did not work with water. Instead, we have to look for something with a circuit that can be turned on by a touch button or a sensor.
• The sound should start when the circuit is closed and stop as soon as the connection is broken. You want to hear something as soon as the probe touches water and stops as soon as it no longer touches water. The toy I found was a fake phone that would play sounds that would continue after the button was no longer pressed. That makes it difficult to find the exact water level, although it could be done with some extra patience.
• It should be small enough to fit in the container you want to use for the probe. It is ok to cut the sound generator in several parts, as will be shown later. In my case, I had a really narrow tube in my test set-up and I could not take the smoke alarm apart in sufficiently small parts to fit it all in. If your well is much larger, than the construction will likely be easier.
• It should be cheap.

In my case, the best choice was an alarm that would go off when a window or door was opened. The alarm could be opened by loosening one screw, showing:

1. Piezo buzzer that makes the actual sound
2. Circuit that drives the piezo buzzer
3. Battery compartment

I used the original cell batteries but you may choose to use larger ones that hold more energy so it will take much longer before you have to open the container to replace the batteries when they are empty after some use.

The alarm did not fit my container so I cut it up in three parts, the piezo-buzzer (1), circuit (2), and battery compartment (3). When removing a piezo-buzzer, be gentle because it consists of a thin ceramic layer on a metal disk so when it is bent the ceramic layer quickly breaks.

Solder connection wires to the points on the circuit that need to be connected to turn on the sound. This may take some experimenting and searching. If you can see a switch or button, connect a wire to each end of the switch or button and test to see if the sound is turned on when the two wires touch. This is also the moment to test if it will work with water by dipping the ends of the wires (4 in photo) into some water. If this is the case, the rest is just some patient tinkering. If the device has a main switch to turn the complete device on and off, make sure it is secured in the "on" position or, as I ended up doing, solder a wire across to make sure it is always closed.

If you have never soldered before, check out some introductions at Instructables, such as https://www.instructables.com/id/How-to-solder/. Practice on some wires before you start work on the actual project.

Make small holes for the stiff copper wires in the bottom of the probe with the hobby knife. It is easier to fit the wires through if the stiff copper wires are a bit longer. Later, these will be shortened.

Solder the connecting wires (4 in Photo A) to the two stiff copper wires (5 in Photo A).

You want to add some extra weight to the probe, for example by adding some dry sand or pebbles. This makes lowering the probe in the well a bit easier as the measuring tape will be taut. Close the container and test once more to see if all is still working (Photo B).

Cut the stiff copper wires so they stick out about one or two centimeters. Carefully glue them in place with the hot glue, making sure that it is all water tight (Photo C).

Attach the probe to the measuring tape with some strings and/or tie wraps. You can use anything for this but make sure it holds, otherwise your probe may end up at the bottom of the well. Test the connection before you lower it in the well!

It is now time to go out and test the probe in your well! I made a small set-up with a tank, some gravel, and a PVC tube that plays the role of well. I added some blue water paint to the water to show the ground water table. The video shows that it is really easy to find the exact spot where the probe touches the water, much easier than with the traditional bell. You can read the measuring tape at a fixed point at the top of the well but be sure to add the extra length from the bottom of the probe to the zero on the tape.

Happy measuring!