Singapore's national water agency PUB (Public Utilities Board) is calling for proposals for building another plant to produce highly purified water from waste water, known as NEWater, it said on Friday.

It will be the third NEWater plant in Singapore.

NEWater is highly purified water produced with membrane technology. It is drinkable and, more importantly, used in industries that require highly clean water.

The new plant in Changi, to be completed by 2016, will add an additional capacity of 50 million gallons (228,000 cubic meters) per day to the city state's NEWater capacity.

Its main process facilities will be built mostly on the rooftop of the Changi water reclamation plant, saving both land space and cost. The successful bidder will enter into a 25-year agreement to supply NEWater to PUB from 2016.

Singapore has been faced with a shortage of natural fresh water resources due to its limited land area as a small island state and used to depend on imported water from Malaysia. However, it has managed to achieve the capacity to be self-sufficient by harvesting rainwater and tapping into waste water treatment and desalination.

NEWater currently meets about 30 percent of Singapore's water demand with a combined capacity of 82 million gallons per day (373, 920 cubic meters). The long term goal is 55 percent. Endi