The Tuas Desalination Plant is the world's most space efficient in terms of the amount of water it can purify for its size, said national water agency PUB.

At 3.5ha, it is the smallest of the country's desalination facilities, yet it produces 30 million gallons of drinking water a day, the same amount as SingSpring Desalination Plant, which is almost double its size.

It took two years to build and opened officially yesterday. And now that it is running, 30 per cent of Singapore's water supply can be met through desalination.

The $217 million facility will remain the smallest even after the next two desalination plants are built in Marina East and on Jurong Island by 2020.

It is the first to use solar power, as well as the most technologically advanced. More than 7,000 sq m of the new plant's roof will be covered by a photovoltaic system and, when online, the solar panels can generate 1.4 million kilowatt hours of energy a year, enough to power over 300 four-room flats for the same period.

However, in an indication of just how much electricity is needed for desalination, this is enough to run only the plant's administrative building - less than 1 per cent of the facility's total needs.

The Tuas Desalination Plant combines two purification methods used separately in SingSpring and Tuaspring. By doing so, its reverse osmosis membranes - where the final stage of purification occurs - must be cleaned only once monthly, compared with as often as once every two weeks.