Experts found more than 4kg of the drug in samples of water - which would suggest 40,000 "doses" a day are being taken in an area where the number of cocaine users was thought to be closer to 15,000. The tests were carried out on water in the River Po valley, which stretches across northern Italy from Turin to Venice, passing through the centre of the fashion capital, Milan. The survey showed just how prevalent cocaine use was in the area, which is considered to be the wealthiest region in Italy with the largest proportion of working young people aged between 17 and 34. Experts said 4kg of cocaine a day would suggest an average daily use of at least 27 doses of 100mg of cocaine for every 1,000 young adults. This equated to at least 40,000 doses being taken every day and indicated cocaine with a street value of 60 million was being consumed in the region each year. Details of the survey, which was carried out by the Mario Negri Health Institute in Milan, were published in the scientific journal Environmental Health. As well as riverwater, scientists tested the water flowing through sewers and treatment plants between February and April this year. According to ministry of health estimates, of the five million people who live in the area, 15,000 are considered regular cocaine users. The figures are based on medical records and crime statistics, but the latest research would seem to suggest a much higher figure. In their tests, scientists checked water for the cocaine by-product benzoylecgonine, which is excreted in the urine of users of the drug. "Our main goal was initially to verify how our consumption estimates compared with official figures," Ettore Zuccato, from the Mario Negri Institute, said. "We expected our field data on cocaine consumption to give estimates within the range of the official estimates, or perhaps lower, but certainly not higher. "Cocaine users pass about 5 per cent of pure cocaine through their urine and 50 per cent as a by-product, so with the right equipment it is easy to look for these products. "What it also shows is that the most disturbing aspect of the study is that cocaine abuse is a lot more widespread than ministry of health figures would suggest - at least three times more - and is obviously underestimated. "The tests were carried out in water from the River Po and from sewage plants. No trace of cocaine was found in drinking water supplies," Mr Zuccato added. "Next year, we hope to expand these tests and look for the presence of heroin, cannabis and amphetamines."