HOW IS THE WASTEWATER RECYCLED?

- A combination of reverse osmosis and disinfection with ultraviolet radiation is the most common method. In reverse osmosis, water is forced through very fine membranes that filter out salts and other matter but let water molecules pass through.

WHO IS ALREADY DRINKING IT?

- Singapore opened two NEWater sewage-recycling plants in Feb. 2003. They add treated water to its reservoirs to provide about one percent of the island's total daily water consumption.

- Greater London does not formally add wastewater to its potable supply. But its 13 million residents joke their water has already been through five people before coming out of the tap, because towns upstream such as Oxford and Reading discharge their treated sewage into the River Thames.

WHAT'S THE BENEFIT?

- Wastewater has been recycled and used for watering parks and golf courses for decades. Using it to top-up drinking water supplies is seen as the next step to sustain the world's over-stretched water supplies.

ARE THERE ANY DOWN-SIDES?

- As well as the psychological "yuck" factor of drinking former sewage, experts say such water purification projects use a lot of energy. There are also environmental issues about disposal of the concentrated salty waste water by-product.

BETTER THAN THE REAL THING?

- Informal taste surveys have found most people can't tell the difference between tap, recycled and bottled water.

- A 2001 University of Southern Florida study found the microbiological quality of water from a wastewater treatment plant was better than that from the local reservoir.

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