Dr. Seán Ó hÓgáin:

That is the first tap. The first tap provides rainwater. The second tap provides water that comes from Malaysia. This water is still available under an agreement. The third tap provides sewage water that has been transferred to a water treatment plant and put through microfiltration and reverse osmosis to produce what the authorities in Singapore call "NEWater". They undertook a political drive to get people to accept this water, which is of a potable standard. Some of it is put into the water system and part of some of it is sold to high-tech industry. The fourth tap provides water that has been subject to desalination. The "four taps" approach refers to the four ways in which water is supplied in Singapore.