STARBUCKS was blasted by environmental experts last night after The Sun discovered it pours millions of litres of precious water down the drain at its coffee shops.The giant coffee chain has a policy of keeping a tap running non-stop at all its 10,000 outlets worldwide, wasting 23.4 MILLION litres a day.That would provide enough daily water for the entire two million-strong population of drought-hit Namibia in Africa or fill an Olympic pool every 83 minutes.Every Starbucks branch has a cold tap behind the counter providing water for a sink called a “dipper well”, used for washing spoons and utensils.Staff are banned from turning the water off under bizarre health and safety rules — bosses claim a constant flow stops germs breeding in the taps.Starbucks has built up a massive chain, popular with coffee drinkers from Hollywood stars to builders, and proudly boasts of its work for the environment.But water companies accused the firm of HARMING the environment by frittering away a vital natural resource.ClaimAnd the claim that running taps are needed for hygiene reasons was dismissed by experts as “nonsense”.Starbucks has 698 branches in Britain, each open for 13 hours a day.Even a slow flowing tap spurts out at least three litres of water a minute, meaning UK Starbucks are wasting an estimated 1.63 MILLION litres a day.That is the daily water requirement for a town the size of Matlock, Derbyshire.And water shortage is seen as one of the major problems facing the world.A single Starbucks tap left running for just over three minutes wastes the amount of water one African needs to survive for a day in drought conditions.The Sun investigated after a Starbucks executive revealed the policy in a letter to a couple who complained about a tap left running at their local branch.Lisa Woolfe, 39, of Cuffley, Herts, said: “I noticed a small sink behind the counter had its tap running. The assistant said the store was told to keep it running as it cleaned the pipes.I could not believe it but when we contacted head office, they confirmed that the taps were left on and the water was not recycled.“It is an absolutely astonishing waste of water, especially for a company which prides itself on its green credentials.”Our undercover team checked Starbucks outlets across the UK and around the world and found some baffled staff did not use the running tap and did not even know what it was for.At Starbucks in Covent Garden, London, a worker shrugged and said: “We’ve got to keep it like that. I don’t know why.”In Bristol a tap was seen running full on for 15 minutes.Similar scenes were witnessed in Derby, Nottingham, Manchester, Birmingham and Bath.On 52nd Street New York, a tap was running the whole time our investigators were there and nothing was cleaned under it.It was the same in Los Angeles and in Sydney, Australia.Australia is in the grip of a seven-year drought which is the worst for a century.Staff at one of the 50 Starbucks in Beijing, China, threatened to call cops as we photographed a running tap.A spokesman for UK Water, which represents water companies, was horrified by our findings.He said: “It is wasteful and unnecessary. There is absolutely no need to keep taps running.”Peter Robinson, of environmental charity Waste Watch, said: “Leaving taps running all day is a shocking waste of precious water. And to claim you are doing it for health and safety reasons is bonkers.“Tap water comes from rivers and groundwater and wasting it can cause great harm to the environment and wildlife. Big companies should set an example.”Jacob Tompkins, of independent water efficiency agency Water Wise, said: “If they are doing all their basic cleaning procedures, I fail to see why they would need to do this.“There are a lot of other ways to stop a build-up of bacteria.“The chance of a build-up in the spout is extremely remote. And if there is one they’re not cleaning the tap properly.”Ian Barker, head of water resources at the Environment Agency, added: “We are already taking too much water from the environment and are seeing reduced river flows.”In Vienna, Austria, Starbucks staff confirmed the tap was always left running.In Cluj, Romania — also hit by a drought — a Starbucks worker said of the tap: “We don’t know what it is. Nobody ever uses it.”