Use water wisely, avoid waste, and recycle wherever possible.

This was the message from Prime Minister Lee Hsien Loong on Facebook yesterday, as he related the worrying sight that greeted him as his flight passed over Johor's Linggiu Reservoir en route to China two weeks ago.

PM Lee had taken a photograph which he posted on Facebook showing the water level in the reservoir at a record low of 25 per cent after several years of low rainfall. Alongside it was a satellite image from Google Earth showing the reservoir at full capacity.

"The difference is stark, and worrying," said PM Lee.

Built and run by Singapore's national water agency PUB, the Linggiu Reservoir is allowed to supply up to about 60 per cent of Singapore's current water needs, as provided by the Separation Agreement between Singapore and Malaysia.

Besides water imported from Malaysia, Singapore diversifies its water sources across three other national taps - local reservoirs, Newater, which is treated wastewater, and desalination.

"Singapore is fortunate to be sheltered from many natural disasters, but our water supply is still at the mercy of the weather," noted PM Lee. "Our Four National Taps have mitigated this, but we must still do all we can to conserve water."

The world has been experiencing one of its strongest episodes of El Nino on record, which has contributed to hot weather and dry spells in Malaysia.

However, it is expected to be followed by La Nina next year, with prospects for higher rainfall.

Many Facebook users echoed PM Lee's sentiments, while others offered suggestions such as deepening reservoirs at home, tapping into groundwater reserves, and even building specialised towers to condense water from the humid tropical air.

Lin Yangchen