When the parents of Sally Le Page, a British evolutionary biologist, tried to get help from their local water company with installing a new pipe, they were greeted with a bizarre sight.

"My parents couldn't believe their eyes," Le Page wrote in a blog post, "when they saw the man from [the company] Severn Trent slowly walking around holding two 'bent tent pegs' to locate the pipe."

The technician was attempting to use divining rods - a discredited medieval witchcraft technique that was once believed to able to locate water. (The rods allegedly cross when they're above water.)

And it wasn't a one-off.

Ten out of twelve British water firms still use "water dowsing," despite no reputable scientific evidence that it works.

Le Page tweeted at the "all ten major water companies in England and Wales, plus the government-run agencies in Scotland and Northern Ireland," and asked them whether their technicians ever use divination or dowsing rods.

Of the 12, 10 said yes.

"I believe sometimes they do," Northumbrian Water, one of the 10 private companies asked, said in response, "our field services manager tells me he's seen them used successfully before."

"We do have some techs that still have them in the van and use them if they need to," said Severn Trent.

"There have been occasions where we've used dowsing rods," Anglian Water added.

Of the 12, only Wessex Water and Northern Ireland Water said they did not use the ineffective techniques. (Welsh Water said it did, only to later delete its tweet.)

(You can see all the responses on Sally Page's blog.)

So if divining rods don't work, why do people think they do? It's down to something called the ideomotor effect.

It's when you subconsciously move something without realising it - the same way an Ouija board seems able to answer superstitious users' questions. It's you doing it, even if you don't realise it.

As the United States Geological Survey said, "Case histories and demonstrations of dowsers may seem convincing, but when dowsing is exposed to scientific examination, it presents a very different picture."

"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," Le Page wrote.

She continued:

"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," Le Page added.

This article was originally published by Business Insider.

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