Singapore, a small island city-state with some 700 km2 in land area and a population of 4.5 million, is always looking for innovative ways to find new water sources to meet its growing need for water. Rain falling in the urban fringe catchments is not harvested; these areas experience bouts of heavy rain but dry up during the dry season and, as such, the conventional approach of constructing large dams for storage to support large water treatment plants is not economically viable. This paper explores the viability of a newly developed variable salinity water desalination treatment plant to harvest water from estuarine catchments. The plant is able to treat estuarine waters which vary gradually from low salinity river water into high salinity seawater. When the river water has high salinity or dries up, treatment is maintained with the plant operating in seawater desalination mode instead of remaining idle, thus affording high plant utilisation. The treated water is of high grade with energy consumption half that of seawater desalination plants. The average unit production and capital cost of such variable salinity desalination plants is significantly lower than that of seawater desalination plants.