Microfiltration, reverse osmosis and ultraviolet light: how Singapore makes NEWater

Background

NEWater is the name Singapore's national water agency gives to high-grade water reclaimed from treated used water, and it is produced in three stages. First the water passes through membranes in a step called microfiltration or ultrafiltration, which strains out particles and bacteria; a membrane bioreactor can do this job in one step and replace it. Second comes reverse osmosis: very small pores in a semi-permeable membrane let water molecules through while viruses, bacteria, heavy metals and pesticides are held back. Third the water is disinfected with ultraviolet light as a further safeguard. A study in the nineteen-seventies found reclamation technically possible but too costly, and the agency returned to it when membranes improved, commissioning a demonstration plant that made 10,000 cubic metres a day. An international panel of engineers, chemists and biomedical scientists judged the water consistently safe and within both World Health Organization and United States Environmental Protection Agency drinking water requirements, and recommended indirect potable use, meaning it is blended into raw water reservoirs. Four plants are in operation, and the biggest customers are wafer fabrication plants, which need water purer than drinking water and take it through a dedicated pipe network.