Environmental health officers carried out on-the-spot inspections at about 50 stores to ensure fraudulent Zam Zam water was not being sold.
They said the water was known to contain high levels of nitrates and arsenic, was not being sold.
The water is advertised as coming from the sacred well of Zam Zam in Mecca, the most holy city in Islam, and demand increases during Ramadan.
The warning does not cover genuine Zam Zam, which is sourced from the Well of Zam Zam, located within the Masjid al Haram in Mecca.
Councillor Audrey Lewis was concerned Muslims may be exploited into buying counterfeit Zam Zam during the holy month of Ramadan.
She said: “The Kingdom of Saudi Arabia forbids the commercial export of genuine Zam Zam, so we have no idea of the true source of the water which ends up on the streets of the UK.