The presence of water has been the basis for human settlement for aeons, but one ancient method of finding it is still in dispute. Can "an enchanted twig" do the job or do dowsers simply make very educated guesses?
Digging into dowsing
Over the last few weeks a team of experts has been working in a remote part of western Zambia, giving local villages access to the most vital commodity on earth: water. But their expertise is not in geophysics and hydrology. They credit their success to an altogether more unusual talent: an ability to detect the presence of water using the ancient art of dowsing.
David Dixon and his colleagues at the UK-based charity Village Water (www.villagewater.org) have been making the trip to Zambia for five years, paying all their own costs to dowse for water for villages in the arid land near to the border with Angola. Using a variety of methods, including the age-old technique of dowsing rods, the team locates underground streams, and - if they sense the flow of water is high enough - telling the villagers precisely where to install a pump.
The team claims its work has brought water to dozens of communities and more than 10,000 villagers. It's a success story that delights the locals - but leaves many scientists cold. For how on earth can dowsing work? Dowsers like Dixon and his colleagues believe they are tapping into the same mysterious effect exploited by miners, surveyors and prospectors for millennia. According to some sources, the first reference to dowsing can be found in 8,000-year-old cave paintings in Algeria. By the 16th century, dowsing was routinely used by prospectors in Europe searching for new ore resources.
Yet even at the time there was scepticism about its value, with the renowned German mineralogist Georg Agricola arguing that someone "prudent and skilled in natural signs" should have no need of "an enchanted twig". Even sceptics accept that dowsers can find water; the real question is whether they succeed as a result of dowsing - or despite it. One common explanation is that underground water is so ubiquitous that there's a high chance of finding it anywhere. Hydrologists point out that even in apparently arid areas like Zambia, groundwater is often relatively plentiful. Yet dowsers stress they do not simply locate water: they can also estimate likely flow-rates, and even water quality.
So what is the truth about dowsing? Over the years numerous studies have tried to get to the bottom of the dowsing phenomenon, often with controversial results. In the early 1970s, the UK Electricity Research Council (ERC) carried out tests in which dowsers were challenged to find cables and other equipment buried in the ground. The results revealed that the dowsers succeeded at a rate higher than would have been expected if they had merely guessed. To find out more, the experimenters then repeated the tests, but this time with some ERC technical experts who were asked to see if they could spot any clues as to where the hidden objects might be. Remarkably, they too achieved an impressive hit rate - and actually outperformed the dowsers.
It's a result in line with the view of sceptics since Agricola: that the success of water dowsing stems from the sheer ubiquity of groundwater - plus a keen eye for possible telltales, such as the presence of vegetation and the lie of the land. But according to some, a series of studies funded by the German federal government refutes this explanation. The tests, which began in 1987, put more than 300 dowsers through their paces, and appeared to show that their success rate was well above chance expectation. To find out if this was simply the result of dowsers picking up on environmental clues, the team devised a second set of experiments, which took place inside a two-storey barn north of Munich.
On the ground floor the team installed a flexible pipe system through which water flowed - and whose position could be randomly altered. On the upper floor, the dowsers walked along a line and were asked to declare where they believed the pipe to be. To minimise the risk of cheating, the experiment was "double blinded", with neither the dowsers nor the experimenters knowing the whereabouts of the pipe.
This second experiment ran for two years, and involved more than 40 dowsers. And according to the experimenters, the results showed that some dowsers really are able to sense the hidden presence of running water. In their final report, the team reported that six participants showed "an extraordinarily high rate of success, which can scarcely if at all be explained as due to chance". Not everyone was convinced, however. Sceptics pointed out that most of the dowsers performed badly, and claimed that even those who occasionally succeeded were very inconsistent.
They also accused the experimenters of hand-picking the best results from the handful of successful dowsers, thus invalidating any statistical analysis. To this day, the results of the "Munich Experiment" remain bitterly controversial. Perhaps the fairest interpretation is that it confirms the long-standing view that dowsers possess a genuine knack of detecting water - but it's the result of their skill at picking up on subtle environmental clues to its presence.
If environmental clues aren't the explanation, then some other effect must be at work. Some scientists have suggested that the dowsers are sensitive to some kind of magnetic disturbance triggered by flowing water. Others have argued for the existence of a wholly new force of nature, dubbed the "D-force", which draws dowsers to their target. Whatever the truth, the controversy over the scientific basis of dowsing looks set to continue. It must all seem hopelessly academic to the villagers of Zambia.
For them fresh water is far more important than watertight explanations. Robert Matthews is Visiting Reader in Science at Aston University, Birmingham, England