Tap water was off the menu yesterday at Raffles City, with restaurants and food outlets complaining of an odd-smelling liquid that looked yellowish and cloudy.
All the outlets The Straits Times spoke to said they had to serve bottled water to guests.
On the ground floor, restaurants Brotzeit, Marche and Salt Tapas & Bar were all affected.
"We opened for breakfast this morning, and the water was slightly cloudy and it tasted off," said Ms Haida Hanim, a manager at German restaurant Brotzeit.
The afternoon heat had guests asking for iced water, so staff had to apologise and offer to sell them bottled water instead, she added.
"People were asking if the tap water was safe to drink... The taste was weird so we didn't want to take chances."
At Marche, staff were even using bottled water to mix drinks.
Basement outlets, including Mos Burger and Korean restaurant Bibigo, were affected as well.
Customers did not seem put off, however, and late in the afternoon, outlets began to fill up.
Australian tourist Trevor Prebble, 60, nursing a beer at Marche, suggested: "They must've been doing some work with the plumbing and disturbed it somehow."
Mr Jacke Chye, Raffles City Singapore's marketing communications head, said the mall was investigating the cause and "will continue to monitor the situation closely and put steps in place to prevent a recurrence".
He said four restaurant tenants had notified the mall's management yesterday morning that their water supply was yellowish.
"We immediately proceeded to flush their water system and install additional filters, and clear water supply has been restored," he noted.
The water tanks at the mall are cleaned regularly, and the tank in question had been cleaned two weeks ago and its water certified safe by the authorities.
Water authority PUB said it had not been informed of water quality issues, but was working with Raffles City's building management to investigate the issue.