The tests were taken during a Saturday night in January as part of a television series on cocaine use among Swedes, of whom around 200,000 are reported to have tried the drug.
Sewage water from the inner city and the southern suburbs was tested for traces of cocaine and benzoylecgonine (ecgonine benzoate), which is a bi-product left after the body breaks down the drug.
The samples were sent to Karolinska University Hospital in Solna for analysis.
“The tests show that the equivalent of 10-20 (100mg) doses flows into the water system per hour,” Olof Beck at the hospital told the programme.
Cocaine available in Stockholm is known to have been diluted fivefold and so the programme was able to calculate that 3,000 doses were consumed during the evening – 2,000 in the inner-city and 1,000 in the southern suburbs.
The method is one which has been applied in the USA, the UK and Italy, among other countries, but is the first time that it has been used in Sweden.
“The method is totally reliable,” Olof Beck told the Kalla Fakta.
A test conducted in the Norwegian capital Oslo in 2007 showed that 8,000 doses are consumed daily. A previous test on the water of the Po river in northern Italy showed that around 40,000 doses of cocaine were consumed in a catchment area of five million people.