Daily water use during the current dry weather has shot up 5per cent above average, said Minister for the Environment and Water Resources Vivian Balakrishnan on Friday.
If this goes on, Singapore will have to "re-evaluate the adequacy of our current plans", he said.
He was responding in Parliament to Mr David Ong (Jurong GRC), who asked at what point the country may have to consider water rationing, last seen in the 1960s, if the dry spell persists.
Average water consumption has risen from 400 million gallons a day (mgd) to 415 mgd, as reported last week, and now 420 mgd, a 5 per cent rise in total.
The heavier usage is from both businesses and residents, said national water agency PUB, which has urged cuts in water use.
Singapore is enduring one of its longest-ever bouts of dry weather, with little rain since mid-January. Last month was the country's driest in 145 years.
PUB chief executive Chew Men Leong said at a separate event on Friday that the board was reviewing its options should consumption continue to rise.
In Parliament, Dr Balakrishnan reiterated that water rationing is not needed in "the foreseeable future", if people do their part to save water and cut usage.
Still, he is "taking seriously" a suggestion from the public to run water-rationing exercises. This would remind people of the value of water, he said, and allow them to rehearse rationing procedures.
"On the one hand, we have what I define as a margin of safety (from desalination and Newater). But I'm equally aware that conveying to Singaporeans (this) also carries a risk of complacency."
Singapore's two desalination and four Newater plants have been running at near full capacity during the dry spell, to provide about 55 per cent of the country's water needs.
Dr Balakrishnan said it was "sobering" to note that this additional capacity came about only in the past decade, with the second desalination plant opening just six months ago. Despite Singapore's water technology investments, imported water from Malaysia "remains an essential part" of the water supply, he stressed.
The over $300 million Singapore spent to build Linggiu dam across the Johor River in 1990 - after Malaysia gave the go-ahead - has enabled the Republic to draw 250 mgd of raw water even during this dry spell, he noted.
Singapore aims to achieve water self-sufficiency by 2061, he added, the year the second water agreement with Malaysia expires.
He reiterated Foreign Minister K.Shanmugam's remarks on Thursday that both countries have to honour the agreement.
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