Turning sewage into ultra-clean water

Giant pumps whir deep underground at a plant in Singapore that helps transform sewage into water so clean it is fit for human consumption while reducing ocean pollution. 

The tiny island nation has little in the way of natural water sources and has long had to rely principally on supplies from neighbouring Malaysia.

To boost self-sufficiency, the government has developed an advanced system for treating sewage involving a network of tunnels and high-tech plants.

Recycled wastewater can now meet 40 percent of Singapore's water demand -- a figure that is expected to rise to 55 percent by 2060, according to the country's water agency.

While most is used for industrial purposes, some of it is added to drinking water supplies in reservoirs in the city-state of 5.7 million people.

And the system helps reduce maritime pollution, as only a small amount of the treated water is discharged into the sea.

This is a contrast to most other countries -- 80 percent of the world's wastewater flows back into the ecosystem without being treated or reused, according to UN estimates.

"Singapore lacks natural resources and it is limited in space, which is why we are always looking for ways to explore water sources and stretch our water supply," Low Pei Chin, chief engineer of the Public Utilities Board's water reclamation department, told AFP.

One key strategy is to "collect every drop" and "reuse endlessly", she added.