The study, which was done by the Drinking Water Inspectorate, found that the water contains benzoylecgonine, the form of cocaine created after it has been metabolized by the body.
Substantial amounts of ibuprofen and carbamazepine, a drug used for treating epilepsy, were also found in the water.
"We have the near highest level of cocaine use in western Europe," drug policy expert Steve Rolles told The Sunday Times. "It has also been getting cheaper and cheaper at the same time as its use has been going up."
The study found the drinking water also contained caffeine.
"Intakes of the compounds detected in drinking water are many orders of magnitude lower than levels therapeutic doses," said the report. "Estimated exposures for most of the detected compounds are at least thousands of times below doses seen to produce adverse effects in animals and hundreds of thousands below human therapeutic doses. Thus, the detected pharmaceuticals are unlikely to present a risk to health."
Almost 700,000 people aged 16-59 are estimated to use cocaine annually in Britain.