What made the incident worse was that after she left the restaurant with her boyfriend, Nando's staff started clapping, she claimed.
The 28-year-old actress, incensed by the fact she had been asked to pay S$3.90 for a cup of warm water, vented her frustrations on Twitter later that night.
"Somebody please save this restaurant. They have no idea what service and initiative means," she tweeted via @JoannePeh, triggering a flurry of comments from her 20,000 followers, many of whom supported her.
In an interview with Yahoo! Singapore three days after the incident, Peh reiterated that the underlying issue is not whether the restaurant plans to charge customers for tap water or not.
"I don't want to come off like I'm very petty... but the clapping was what I felt was most uncalled for in the whole string of events," she said.
"A lot of people have asked me, 'why did they do that?' I don't know, I'm just as bewildered. Their behaviour is so bizarre, even Nando's can't explain it either. I also want to know why."
"Different establishments have different rules and policies, and I respect that," she added. "But every customer has the right to walk away."
The incident took place when Peh and her actor-deejay boyfriend Bobby Tonelli, 36, went for dinner at the restaurant, which is famed for its grilled chicken. It has three outlets here.
After placing their orders, Peh asked for hot water but was told by the waiter that this was not possible. She then asked to speak to the manager, who said the same.
"The manager actually told us he once got into trouble for serving hot water, which I have never heard of before," she said, reported The Straits Times.
The couple was eventually told that hot water would cost S$3.90, which is the menu price for a cup of tea. However, Tonelli went on to point out that a bottle of water on the same menu only cost S$1.80, to which the manager agreed to charge them that and heat up the bottled water instead.
However, the message was apparently not conveyed to other staff, who were "dumbfounded" when the couple had to request for hot water again.
Finally, when neither their food nor drinks had arrived 30 minutes after being seated, an exasperated Peh and Tonelli decided to leave the outlet.
It was then that Peh said she heard the restaurant's service staff clap and cheer.
"In all honesty we'd have dropped it as another unfortunate experience if not for the fact that they applauded on our way out," said Peh on Twitter.
"The worst thing is the manager clapped too," Peh added.
It was the first time Peh had walked out of a restaurant fuming.
"We are not asking to be treated in any special manner just because we are celebrities. It's just hot water, how hard can that be to serve?" Peh told The New Paper.
Tonelli also said that he and Peh have always tried to be "very low key" in public. This incident, he said, was "certainly not about diva behaviour."
Peh later told Yahoo! Singapore that the online furor seemed to be "opening up a whole can of worms", with regards to other negative reviews of the restaurant that have since surfaced. She suggested that the problem could be "all internal".
"There is a lack of a proper charging system in place, and a lack of proper training," she said. "Service staff needs to know how to handle requests."
Ironically, the last time the couple dined at the restaurant, they received such good service that Tonelli, a Class 95FM deejay, raved about it on air.
Nando's have since called the actress to apologise. It also tweeted an apology the following day and said, "We saw ur tweets abt ur experience and would like to sincerely apologise for this incident."
"We do appreciate and value all our guests' feedback. Your tweets highlighted some issues which we are currently looking into."
Nando's regional marketing manager Fanny Chai has also come forth to explain that it is a "corporate decision not to serve water on the house as beverage sales is a key source of business revenue".
She said that staff members usually offer bottled water or a hot beverage such as tea as an alternative, when customers request hot water.
This was not clearly explained to Peh at the time, resulting in a "misunderstanding", continued Chai.
She also said the restaurant was still assessing the water policy at this point, adding that "it is not true" that a staff member would be fired for serving water to a customer.
As for the clapping incident, Chai declined to confirm details as "internal investigations of the incident are currently underway to understand and verify the situation and chain of events."