Where to start with using water supply lines as communication medium?

[Holes Flow]

Experts,

I want to test the viability of micro-controller communication site-to-site using just metal pipes buried underground. Thought it wise to toss it out first to you lot for comments.

We have metal pipes underground between houses that supply water, and probably the same for gas (in certain areas). While the drain lines can be of any materials, what ways are worth testing for using the supply lines? I'm talking about the actual pipe material as the medium (assuming the water can't?)... The BAUD rate would be ridiculously low, but it might not need to be high. I'd like to investigate, but asking here might be wise in advance.

Q: Is there anything stopping one from using metal supply lines for water to communicate over?
Q: If not, any ideas on which ways to try first?

I'm not talking about using WiFi or traditional radio, but the actual metal supply lines themselves.

Ideas?

[larrybl]

Ummm, Buried metal water lines are considered a physical ground in my area. You may have better luck using the electric lines between houses, Google X-10 devices.
https://www.x10.com/

[CJay]

Have a look at things like 'HeyPhones' as used by cave rescue teams, mentioned here:

http://www.shropshirecmc.org.uk/radio.html

It would seem there are schematics as there are mentions of people building their own

[nfmax]

You mean using acoustic waves, travelling in the steel tube wall? Should be feasible. Lots of effort gone in to analysing tube waves  https://www.glossary.oilfield.slb.com/en/Terms/t/tube_wave.aspxhttps://www.glossary.oilfield.slb.com/en/Terms/t/tube_wave.aspx in (oil & gas) wellbore seismic applications, where they are generally a nuisance.

[Halcyon]

I'm not an EE but I would have thought grounding would be a significant issue seeing as most buried pipes aren't insulated?

[T3sl4co1l]

Yeah, electrically that's not going to happen, unless the water is relatively conductive (not potable??) and the pipes are plastic (which, actually, is pretty common, so maybe not too far out?).

Acoustically, I don't know.  You need to make an acoustic waveguide, which means having a somewhat higher index of refraction on the inside to exhibit total internal reflection, or a significantly higher index of refraction on the outside to make a normal waveguide or conduit.  Water has higher density than plastic, but not by much.  And, I think, a somewhat higher elastic modulus, but it depends.  So, it might work better the other way, even (a plastic fiber, floating in water, carrying acoustic waves?).

I'm... not sure how relevant these concepts are for longitudinal and shear waves (as opposed to the transverse EM waves I'm more familiar with).  The significance by the way, of density and Young's modulus, are that they are equivalent to the inductance and capacitance of free space, and so set the wave impedance, and the local speed of light and index of refraction.  There are different moduli for the different wave modes (in solids; liquids do not support transverse or shear forces), giving different wave parameters, as well as different couplings, between different media, and between the different modes (dispersion).

Tim

[Holes Flow]

@CJay,

This is really promising. They are talking here about going through rock, where a conductive metal pipe should be optimal.

[soldar]

As much as I love a challenge I just can't see the practicality of this. There are many ways of communicating and I'd have to think much to come up with one that is worse.

You might consider using the water pipe as an optical transmission channel. If you have a fairly straight run from one building to the other you could put optical transducers at the ends of the straight run, avoiding all the elbows and valves.

[Holes Flow]

Experts,

I found out more about my local test system/municipality. I will be meeting next week to learn more, and ask smart questions.

-The mains are mostly 16" diameter.
-They are all cast iron or ductile iron (DICL).
-They have a 3 mile (long?) section for testing, with key points already exposed.
-Though a small town (smaller than city), they are losing >25,000 gallons/month, and don't know where.
-They expressed a desire to know the state of key valves, and continuous (periodic) flow and other simple measurements.

-The first system I am inclined to test is induction communication via the pipes themselves, from one key point of interest to the next.
-Going down into LF (30kHz-100kHz) has been tested to have the best trade-offs of distance, power consumption, and penetration through typical ground materials. The HeyRadio uses 10W, for example, at 87kHz, and on a good day can get really good BW for voice and pictures to 500m. I'm only doing data, and the baud can be lopw and still not impact viability.
-I don't know the longest/typical distances these are, but I have access to the diagrams electronically to get an idea. Any place that needs sampling/testing, or has a valve of some kind, or another piece of equipment, is a prime initial location.

I've found that getting AF amplifiers that also go to ~87kHz is not too difficult, and their cost makes benchmark testing induction communication the first choice. Induction will also not be invasive (just a coil around the mains pipe). I haven't done hard-core radio theory in decades, but have been in the microcontroller circles these past years. I am hoping that the fact the iron pipes will conduct better than the surrounding earth materials will be a benefit, perhaps even allowing the earth ground to be a form of return if needed (meaning making a circuit including ground, instead of just a loop/coil at each end.

Does anyone have any questions I should ask of my 'guy on the inside'?

Does anyone have any suggestions for cheap rigs to either build from schematic or modify a ~10w audio amp for benchmarking?

Does anyone want to make any official guestimations on how well (or if) it will work (meaning distance of signal detection)?

TIA!

pat

[Holes Flow]

As much as I love a challenge I just can't see the practicality of this. There are many ways of communicating and I'd have to think much to come up with one that is worse.

Sorry @Soldar,

It isn't everyone's cup of tea. But if it were easy, it would have been done already.

Thanks for your contribution, though!

[Seekonk]

This reminds mo of back when we were doing ultrasonic whistles as a way of seeing flow in liquid sodium.  Couldn't exactly run wires at those temperatures.  Water was much easier to use for early research and only needed a garbage can and a pump.   We would blow the whistle, but results kept getting lower and lower.   Wait an hour and things would work again.  Turns out the whistle was making microscopic bubbles in the water and they absorbed the signal. So watch out for those bubbles!

Years after our town after installed plastic pipe everything started leaking.   The last time I saw a report more water was lost than sold.

[tszaboo]

So any reason not to just place a 4G modem and a sim card on it, instead of spending loads of money on research?

[Holes Flow]

Would 4G have any chance of going through 10' or more earth?

I was under the impression 4G signals were RF, and in the range of GHz: https://www.wpsantennas.com/cellular-frequency-information.aspx

[hendorog]

I'd think water pipe looks like a bit like a round waveguide.

Dielectric is water and probably air.

We know water absorbs microwaves.
Smaller diameter waveguides have lower cutoff frequencies.

So if you could find a freq or freq range where the water didn't absorb the signal and was above the waveguide cutoff then it might work.

The might be other modes which can be used.

[tszaboo]

Would 4G have any chance of going through 10' or more earth?

I was under the impression 4G signals were RF, and in the range of GHz: https://www.wpsantennas.com/cellular-frequency-information.aspx