Singapore's Four National Taps refer to the 4 sources of water supply, i.e. (1) Local Catchment, (2) Imported Water (from Johor), (3) NEWater and (4) Desalinated Water.
The first 'tap' refers to the supply from our local water catchments and reservoirs.
The second 'tap' refers to the import of water from Malaysia under the 1962 water agreement.
Our third 'tap' NEWater, leverages on a 3-stage process of ultra-filtration/ micro filtration, reverse osmosis and ultra violet radiation to reclaim water from our used water effluent.
Our fourth 'tap' is seawater desalination through which freshwater is obtained by desalting seawater through the reverse osmosis process.
The Four National Taps help to diversify our sources of water to ensure a reliable and resilient water supply.