The cocaine byproduct is just one of the many traces of pharmaceutical compounds and other contaminants found in our water – and new contaminants are discovered all the time. But should we really be worried?

According to various headlines this weekend, we Brits use so much cocaine that traces of the drug have been found in our water supply. A study by the Drinking Water Inspectorate (DWI) aimed at assessing the danger from pharmaceutical compounds in drinking water revealed that even after intensive purification treatment, minute quantities of benzoylecgonine – the metabolised form of cocaine – were found at four sites in Britain. So are we a nation of coke-heads? And does the presence of something related to a class-A drug in the water we drink actually matter?

The answer to the first question, says Sue Pennison of DWI, the independent body that ensures the water companies supply water fit to drink, is not clear. Benzoylecgonine, she notes, "is also an ingredient in a popular muscle-rub, and there's no way of telling which it came from".

The answer to the second question is clearer: it is no – at least, not in these concentrations. Traces of all sorts of things can be found in our drinking water, but as long as they are below the levels laid down by the Water Resources Act, which introduced the EU Drinking Water Directive into UK law, the water is deemed safe for human consumption. Those levels are strict: lower – sometimes by as much as 20 times – than those of the World Health Organisation's guidelines, which are themselves set to ensure there would be "no potential risk if the contaminant was absorbed continuously over a person's lifetime".

Thus in a report last year, Public Health England said traces of six pharmaceutical compounds had been found in drinking water: benzoylecgonine, the painkillers ibuprofen and naproxen; carbamazapine, used in treating epilepsy, and its metabolised form carbamazapine epoxide; and caffeine. But, it noted, their median concentrations – which ranged from less than one to 11 nanogrammes per litre – were "at least thousands of times below doses seen to produce adverse effects in animals, and hundreds of thousands below human therapeutic doses. The detected pharmaceuticals are unlikely to present a risk to health."

Scrutinised and audited by DWI, the water companies follow a strictly controlled methodology to test for a total of 39 parameters in UK drinking water, broadly divided into microorganisms (such as viruses, protozoa and bacteria), chemicals, and physical measures like the pH level and total organic content. New contaminants are discovered all the time: a Brunel University study in 2011, for example, raised the alarm about the presence of the dishwasher detergent chemicals benzotriazole and tolytriazole in UK drinking water.

Some, it has to be said, do sound rather alarming: among the chemical contaminants tested for are antimony, arsenic, benzene, cadmium, cyanide, lead, mercury, nickel, pesticides, tetrachloroethene and vinyl chloride. But the point, Pennison says, is that the tests "are there to make sure there's not an issue." And even if the testing programme lets something nasty by, there's a catch-all provision: by law, "water companies cannot supply anything that would cause potential danger to human health."

In her latest letter to the government summarising the findings of the DWI's 2013 report on drinking water quality in England, the Chief Inspector of Drinking Water, Professor Jeni Colbourne, confirmed that fully 99.96% of all tests carried out on public drinking water in England in 2012 satisfied EU and national standards. You may, it seems, swallow safely.