Muslims fasting for Ramadan are being strongly advised to steer clear of any water described as “Zam Zam” – as it could pose a serious risk to health.

Tests have shown that the water, which is advertised as coming from a sacred well in Mecca, could contain high levels of arsenic and nitrates.

Arsenic levels have been almost three times the legal limit in water tested in recent years.

Exposure to the toxin can lead to an increased risk of developing cancer.

As in past years, Tower Hamlets Council has joined forces with the Food Standards to swoop on any shops or individuals selling the brand.

In its true form, the water comes from a well in the holy Saudi Arabian city, but under Saudi law it is not allowed to be exported from the country.

Many bottles purporting to be Zam Zam on sale in London and the rest of the UK are likely to be from another source.

A council spokesperson said: “People should consider avoiding drinking any water described as Zam Zam because there is no completely safe level of arsenic in water – and the more arsenic consumed the greater the risk.

“However, if anyone has occasionally drunk small amounts of this Zam Zam water, the risk to health for adults and older children would be very low.”

Children are also more sensitive to nitrate so it is strongly recommended that they are not given the water to drink.

Many in the East End’s Bangladeshi and Somali communities began the 30 day fast on August 1.

If you spot an individual or business selling Zam Zam call 020 7364 5008 and they will be investigated.