Ancient underground wells in water-deprived Jordan have 20 times more radiation than is considered safe for drinking, researchers said, raising concern about water safety across the Middle East.

Their study showed that water from an underground source in Jordan contained high levels of a naturally occurring radioactive particle linked to some cancers, posing a health risk to thousands of people in central Jordan who drink it.

Several other Middle Eastern countries have recently tried to offset water shortages by tapping similar underground reservoirs, as growing populations have overwhelmed supply.

This could expose people in Israel, Egypt, Libya and Saudi Arabia to high levels of radioactivity because these countries tap similar sources for drinking water and agriculture, researchers said.

'It's water you don't want to drink,' said Avner Vengosh, a researcher at Duke University in the United States, who led the study published in Environmental Science and Technology.

'Several studies have shown it is associated with high levels of bone cancer. Others have even shown some association with leukaemia.'

Vengosh and colleagues examined water samples from 37 pumping wells in the Disi aquifer, along Jordan's southern border with Saudi Arabia, for signs of radioactivity.

Jordan has expanded exploitation of the Disi aquifer as its annual water use exceeds the capacity of its major river, the Yarmouk, and over-pumping has made other sources too salty.

Officials had thought the low salt content of the pool Vengosh's team looked at made it an ideal source of drinking water. But further tests showed the water contained high levels of naturally occurring radium, a radioactive particle.

'Ironically, the high quality of that water is what makes it suitable for drinking,' Vengosh said in a telephone interview.

The findings have implications for several Middle Eastern countries facing water shortages which have turned to similar ancient underground sources for supplies of fresh water.

'We suggest that high-radioactive groundwater may also exist in these basins,' the researchers said in a statement. 'This could pose health risks for a large population.'

Libya is exploiting one aquifer on a massive scale, Israel is using one for farming purposes and Jordan recently launched its $600 million project to pump drinking water from the Disi aquifer toward Amman, a city of 3.1 million, Vengosh said.

The researchers recommended that health officials in the region monitor the level of radioactivity in their water supplies, particularly in Jordan where there is no official monitoring at present.

'There is a huge level of unawareness among the population,' Vengosh added.-Reuters