Britain's Food Standards Agency (FSA) warned that Zam Zam water, which is sacred to Muslims, is being fraudulently sold with almost three times the permitted level of arsenic - thought to be a cancer-causing substance.
The batches were seized in London's Borough of Westminster, but the FSA said that "other brands of Zam Zam water are thought to be on sale in the UK and could be contaminated".
It is illegal to export Zam Zam water from its native Saudi Arabia for commercial sale, although it can be brought into the UK by returning pilgrims for personal use.
The local authorities in Westminster have now ordered the importer, Amazon Communicate, to stop importing its Natural Zam Zam water.
Yet, more fraud problems in alcoholic drinks suggest that fake products are still a serious problem on the UK drinks market.
The FSA announced Friday that authorities had seized fake vodka after police raided an illicit brewery in northern England. Samples found no methanol contamination, but that stated alcohol levels were wrong and differed from those stated on genuine versions.
The brands affected included Tamova, Kommissar and Hanacka vodkas, while labels and no products were found for Glen's Vodka and Imperial Stag Whiskey.
The fraud problem has become such that the UK-based Gin and Vodka Association and the Scotch Whisky Association announced they would sign an agreement with the UK customs office (HMRC) to increase their fight against black marketers.
"UK spirits producers will be actively working with HMRC to tackle the spirits fraud problem; particularly the large scale organised freight diversion frauds, which deprive the government of millions of pounds of revenue each year," said the Gin and Vodka Association.
Director general Edwin Atkinson said that "because gin and vodka is the largest sector in the UK spirits market, the industry is well placed to provide information that could have a significant impact on spirits fraud and these agreements reflect this".
UK chancellor Gordon Brown laid out a range of measures to beat alcohol fraud in this year's budget, including the introduction of official stamps for spirits and infiltration of supply chains.
The European Commission announced recently that seizures of fake food and drink products entering the EU rose by 200 per cent last year. Lipton, Coca-Cola and Nestlé products topped the list.