Water levels in Linggiu Reservoir in Johor have fallen to an all-time low of about 43 per cent, and Singapore could take the unprecedented step of restricting all non-essential use of water if the situation does not improve.

Dry weather has caused a depletion of water in the reservoir over the past year. In August, water levels dropped to 54.5 per cent of the reservoir's capacity.

The Linggiu Reservoir plays an important role as it helps to supply water from Malaysia to Singapore.

In 1994, Singapore built the reservoir upstream of the Johor River, so that it can collect and release rainwater to push seawater back into the sea. This ensures that the river water is not too salty to be treated by the Singapore-run treatment plant there.

Under a 1962 agreement, Singapore can draw up to 250 million gallons of water a day from the river - meeting up to 60 per cent of its current needs.

Announcing the critical water levels last week, Minister for the Environment and Water Resources Masagos Zulkifli said low levels of rainfall this year have affected both the Republic's and Johor's water supply. Water rationing exercises are ongoing in many parts of Johor, he added.

For sure, national water agency PUB has developed the "Four National Taps" - desalinated water, Newater, imported water and water from local catchment areas - to ensure that Singapore is not reliant on just one source of water.

As senior research fellow Cecilia Tortajada, of the Institute of Water Policy at the Lee Kuan Yew School of Public Policy, said: "Even though a prolonged drought would have impact on Singapore, the fact that the city-state does not depend only on the reservoirs gives it a series of alternatives."

PUB is also exploring the use of underground space for drainage and water storage.

Besides the alternative water sources, it is also hoped that the onset of the north-east monsoon, likely next month, will bring more rain. But Singaporeans should not wait till then to do their part - it is never too early to start conserving water.