Water levels in the Linggiu Reservoir in Johor, which helps to meet half of Singapore's water needs, have fallen to a new historic low.
The reservoir is just over one-third full. Last October, water levels in the reservoir already reached a low of 41 per cent, but they have fallen some more to 36.9 per cent.
These levels are far below the 80 per cent that the reservoir in Malaysia had at the start of last year.
Environment and Water Resources Minister Masagos Zulkifli told Parliament the drop was due to dry weather: "This has impacted the reliability of imported water that supplies half our current needs."
He added: "Fortunately, because we have diversified our water resources, we have been able to mitigate the impact of drier weather. But we cannot be complacent."
The Linggiu Reservoir, built upstream of the Johor River in 1994, collects and releases rainwater into the river.
This pushes seawater back into the sea and ensures that the river water is not too salty to be treated by the Singapore-run water treatment plant there.
Mr Gan Thiam Poh (Ang Mo Kio GRC) and Ms Cheng Li Hui (Tampines GRC) were among those who asked about Singapore's long-term plans to ensure water sustainability and resilience to droughts.
Mr Masagos said the Government will continue to "plan and invest ahead of demand" . A Newater factory, which can produce 50 million gallons of water a day, will be built this year and two new desalination plants will be ready by 2019.
Construction of a third desalination plant in Tuas will be completed next year, while the fourth plant in Marina East, which will supply water to the city area, will be ready in end-2019.
Water agency PUB is also exploring building a fifth desalination plant on Jurong Island.
Some 430 million gallons of water are needed here daily. Demand could more than double by 2060.
Prime Minister Lee Hsien Loong posted on his Facebook page last night that water "has always been and will always be a strategic issue for Singapore, which is why I watch the water levels very closely".
"We must continue to conserve and make the most of this precious resource," he said, urging people to do their part by not wasting water.