If you had to work out where to dig so that you didn’t cut off the water supply to an entire town, would you rely on a Ouija board for your answer? Probably not, but that is in effect what at least two UK water companies (now ten out of the twelve UK companies, see update below) openly admit to doing in 2017. Except instead of asking a Ouija board, they are asking divining (or dowsing) rods.

My parents were trying to install a new water pipe from the mains, which required knowing where the existing mains water pipes were underground. After calling out a technician from Severn Trent, the water company that services the whole of the Midlands, my parents couldn’t believe their eyes when they saw the man from Severn Trent slowly walking around holding two “bent tent pegs” to locate the pipe.

Using divining rods to “find” water in the desert

For the uninitiated, water dowsing is where you walk over some land while holding two L-shaped rods in your hands parallel to each other, and when you walk over a patch of underground water, the rods ‘magically’ cross. When the technique was invented 450 years ago, they probably thought it was witchcraft. Indeed, another name for dowsing is “water witching”.

This was drawn in the 1700s, but modern water companies still think this magic works

However, 450 years and the development of the scientific method later, and we understand that this phenomenon is caused by the ‘ideomotor effect’, the same effect that makes the glass on a Ouija board move without anyone pushing it.

Paper discs disproved Ouija boards as far back as 1853

The ideomotor effect is when just the act of thinking of something causes your muscles to move seemingly ‘on their own’ or ‘reflexively’, without you consciously deciding to move. You can easily test this out yourself. Grab a nearby pocket watch on a chain — or a mobile phone on the end of a charging cable if for some reason you don’t own a pocket watch — and carefully dangle it from your outstretched arm with as long a cable as possible. Now, hold your arm as still as possible and ask yourself a yes/no question. If the pendulum swings anticlockwise it means yes, clockwise means no.

I’ve done this myself, and despite knowing that there’s nothing supernatural, it still ‘works’. That’s the power of the ideomotor effect: even when you know you’re moving it, you can’t feel that you’re moving it. With a Ouija board, it might feel like the glass is moving itself, but in reality, you’re subconsciously making small movements in your arm that push the glass across the board. With divining rods, it’s very tricky to keep long rods like that steady, so even the tiniest muscle movements in your hands will be amplified into large movements in the rods.

However, and here’s the crucial bit, just because the rods move doesn’t mean they are moving in response to water underground. The rods move when the person subconsciously moves their hands. Sometimes this will coincide with water underground, sometimes not. Let’s be honest, in the UK, you don’t have to dig very far to reach water regardless of where you look. All of us are hard-wired for confirmation bias, so we remember the times when dowsing successfully found water, forget all of the times it failed, and ignore how easy it is to find water without even attempting dowsing.

Every properly conducted scientific test of water dowsing has found it no better than chance (e.g. here, here, and here, nicely described here). You’ll be just as likely to find water by going out and taking a good guess as you will by walking around with divining rods. And it’s not for lack of testing; there was even $1 million up for grabs for anyone who could provide rigorous evidence that you can find water using dowsing techniques.

So when my parents saw the man from Severn Trent Water trying to locate an underground pipe using divining rods, they were bemused to say the least. This was the message they posted in the family WhatsApp group:

“I’m glad I won” — true family rivalry in the face of pseudoscience

I thought I’d tweet Severn Trent to see if they knew that one of their technicians was using equipment that is known not to work. I assumed they’d apologise profusely, tell me that this wasn’t part of their standard training, ask me for more details so they could chase up this one rogue water dowser and that would be that. But instead I got:

When challenged about this, they even doubled down, confirming that they use divining rods “when they need to”:

That’s Severn Trent there, a FTSE 100, state-owned water authority that supply about 4.5 million households in the UK, repeatedly confirming that their technicians own and use divining rods. They confused the matter by conflating divining rods (which don’t work) with listening sticks (which can ‘hear’ a leak if you already know where the pipe is), but ultimately are still happy to let people know that they use dowsing.

One of my Twitter followers decided to ask his own water authority, Yorkshire Water, who service 2.3 million households whether they use divining rods.

At this point, I honestly don’t know which is worse: Yorkshire Water openly stating that they use divining rods, or using a GIF that says “MAGIC” when justifying it.

I can’t state this enough: there is no scientifically rigorous, doubly blind evidence that divining rods work. That’s how my scientist side would describe it. My non-scientist side would describe it thus: divining rods do not and will not work. Even now, any explanations of water dowsing rely on the supernatural, and in 2017, I am astonished to find two water companies relying on (and paying for) the supernatural to find underground pipes.

You could just laugh this off. Isn’t it a bit silly that big companies are still using magic to do their jobs! Except if they get it wrong, that could mean the difference between an entire town having safe drinking water or not. If they use divining rods to decide that there isn’t a pipe underneath and so it’s safe to dig there, they could rupture the mains water supply for thousands of people. Not to mention the cost of sending out a “trained” technician to examine a site for several hours, only to get no valuable information. Money that comes from the UK homeowners who have no choice over which water company to use.

Maybe it’s time to leave the magic and divination to Harry Potter.