It was a home remedy for stomach discomfort Mr Gunalan Perumal had taken countless times.

But when the 55-year-old operations manager took a swig of omum water on Aug 3 to treat his indigestion, he ended up in the intensive care unit at the Singapore General Hospital for three days, with injuries and swelling in his mouth and throat.

Preliminary investigations by the Health Sciences Authority (HSA) found that the Sri Ambikkas Omum Water Mr Gunalan had consumed had a pH level of more than 13 - equivalent to levels found in chlorine bleach.

The product is supposed to have a neutral pH of 7.4 to 7.9, said the HSA on Aug 10, after testing additional samples of the drink. "A highly alkaline product may cause adverse reactions, including injuries or burns to tissues (it comes in contact with)," it said, adding that no other poisons or drugs were found in the original sample. HSA was alerted to the case on Aug 4.

The importer has stopped sales of the product. The shop that sold the bottle of drink in question has also stopped selling and stocking it.

The authority said the case appears to be an isolated incident and it has not received any other adverse reports about the drink. The cause is unknown and investigations are ongoing.

Recounting his experience to The Straits Times, Mr Gunalan said: "I drank a mouthful and immediately my throat and mouth started burning. I tried to drink cold water, but started vomiting instead."

The expiry date on the bottle had not passed and its seal was intact before he drank it. In a picture of the bottle that Mr Gunalan showed ST, the drink appeared cloudy, which differs from the usual clear liquid observed in omum water. However, Mr Gunalan said he did not notice this on the day he drank it.

Omum water is made with the distilled oil of the omum herb, also known as Trachyspermum ammi, and is meant to aid digestion. The drink is sold at many mini-marts in Little India.

Mr Gunalan's wife, Madam Tarumampal Mariyappan, who bought the drink from a mini-mart near their Queens Road home days earlier, took a sip of the drink after seeing her husband react to it. "My lips started swelling and I was shocked that it tasted so different," said the patient care assistant.

After Mr Gunalan was discharged on Aug 8, he was given one month of medical leave.

Madam Tarumampal, 55, also received outpatient treatment and was given one day's medical leave.

A spokesman for Sri Ambikkas said the firm voluntarily stopped sales and import of the house-brand drink on Aug 5, after learning about the case on social media. He said the drink's Malaysian manufacturer also produces the same formulation for other brands here.

However, there are other brands of omum water, some made in Singapore, which are not affected.

ST visited 10 mini-marts around the Tekka area, and only three had previously sold the Sri Ambikkas brand of omum water.

One stopped selling the brand a few years ago, and the other two said suppliers told them it was temporarily out of stock about a month ago.

While Mr Gunalan is recovering and feels better, he will be going for a check-up today to determine if the incident left any permanent injury.

The Sri Ambikkas spokesman said it was unable to comment further and will wait until investigations are concluded before contacting Mr Gunalan.