Singapore's second and largest desalination plant, opened by Prime Minister Lee Hsien Loong on Wednesday evening, means the republic now has the capacity to turn seawater into fresh to meet up to a quarter of its entire demand.

The Tuaspring plant at Singapore's far south-western edge is designed, built, owned and operated by Hyflux and can supply up to 70 million gallons of water a day.

Water agency PUB has a 25-year agreement to purchase water from it, starting at 45 cents a cubic meter for the first year.

It also has an attached power plant that is to be fuelled by liquefied natural gas and provides a secure energy supply for desalination.

But while this power plant will be completed by next year, it will begin operating only when it is connected to the national grid, which could take up to 2015, Hyflux said. Next-door neighbour Singspring, opened in 2005, supplies up to 30 million gallons of desalinated water a day.

In all, Singapore uses about 400 million gallons of water a day, which could double by 2060. By then, it aims to have Newater and desalination meet up to 80 per cent of demand.

In his keynote speech at the opening, PM Lee said the Tuaspring plant was the latest milestone in a water journey that has taken place "sometimes over decades", and he urged the audience not to take clean water for granted.