Rainwater Tank Level Meter

In the last few months I've installed four rainwater harvesting tanks around my house. I soon realized that it would help to know exactly how much water is in each of them in order to use them efficiently.

I also quickly found out that water level meters for water tanks can be quite expensive, and almost always involved drilling extra holes into the tank. So I set about making a cheap and easy level indicator which also does not need damaging the tank in any way.

I used the principle that water will rise to the same level in a connected water system at each surface open to the atmosphere. The first picture above illustrates this: The water level is the same height at both sides of the tube I'm holding with ends pointing upwards.

So if we can connect an upright tube outside of the tank, between the outlet and the tap, the water in the tube should rise to the same level as that inside, showing us the exact level of the water in the tank.

That is what I did, and thus far it seems to work perfectly (second picture).

Before we begin, I must just note that I live in South Africa, which means that our water tank systems and accessories may differ in size from those in other countries. But I'm also sure that it would be easy to improvise, using the connections available to you elsewhere in the world.

The first picture shows the connection system I use with all four of my rainwater harvesting tanks. The tanks all come with 40 mm outlets, which I reduce to 20mm in order to connect a tap and ordinary Gardena garden hose watering fittings. At the moment I water my garden from the tanks with an ordinary half inch hose pipe, using only gravity to provide (some) pressure.

The obvious place to tap my connection for the level indicator is the 20mm connecting piece, shown on its own in the second picture.

I used 8mm transparent plastic/PVC tube for the upright indicator part of the level meter. To connect this to the 20mm connector of course requires us to convert the 20mm connector to a T-piece in order to connect the 8mm tube.

I've discovered two ways to do this, which I will outline in the following two steps.

The first method I've devised is to use a cheap and commonly available (at least where I live) part from a micro irrigation system, shown in the first picture. The second picture shows how it is used with a G type micro nozzle for an irrigation system. It is sometimes called a threaded butterfly. The one I used had a top diameter of about 7.5mm.

To make it fit the 8mm hose, I used an appropriate piece of heat shrink tube (third picture) around the top.

To fix the butterfly to the 20mm connector, I found that drilling a 4.2mm hole in the connector works well (fourth picture). The butterfly can then be screwed into the hole, with a generous dollop of contact glue on the threads to ensure a watertight fitting (fifth picture).

Giving the glue enough time to dry, the level meter can than be assembled and fitted to the tank easily (picture second from last).

The last picture shows the installed level meter in its entirety. The top of the tube is fixed to a hole in the tank's overflow plug with a small cable tie. You can of course also fix the tube to a rope or wire around the middle of the tank for extra support.

If you can't lay your hands on a threaded butterfly like I used, there is another possibility, outlined in the next step.

An alternative way of connecting the indicator tube to the 20mm connector is to use an air hose part. This is somewhat more expensive, but probably available anywhere in the world.

The part is called an 8mm BSP male air hose connector, as shown in the picture, already screwed into the 20mm connector via a 12mm hole drilled into the connector. Again a generous helping of contact glue ensures a watertight fit.

A big advantage is that the PVC tube fits quite snugly onto the hose connector. It would also be easy to use an appropriate tube clamp to secure an even tighter fit.

To prevent debris falling into the upright tube, a loose fitting small cap of some kind can be placed over the top of the indicator tube. I used a small vial in which pharmacies provide tablets, with the cap cut off (first picture)

Although the water level is quite clearly visible in the indicator tube, an even better indicator would be something buoyant and colourful drifting on the surface of the water (second picture). I used a piece of cork, spray painted red (last picture).

I hope this instructable was useful, even if only providing some pointers for DIY'ers.