Two-year desalination tests succeed, but officials say only unforeseen events will require HK to adopt the measure Large-scale seawater desalination will not be adopted in Hong Kong in the next 30 years if there is no persistent drought and cross-border supplies remain stable, a water official said yesterday. But the technology could be used on remote outlying islands short of water if it is more cost-effective than installing water pipes. The comments came after the Water Supplies Department concluded a two-year pilot study on seawater desalination in Tuen Mun, which found the technology feasible and safe. The report said it would cost about $2 billion to build a desalination plant on a 10 hectare waterfront site that would supply 5 per cent of the city's water needs, about 50 million cubic metres a year. The cost of the water per cubic metre is about $8.40, compared with $4.50 for treated water from Dongjiang, Guangdong. Electricity accounts for half the cost. Excluding the time needed for approval, a desalination plant could be completed in a year. Introducing the study results yesterday, Bobby Ng Mang-tung, assistant director of water supplies, said although Hong Kong may be far from adopting the technology, the $10 million study was essential to prepare for unforeseen events such as drought. 'There is no urgent need for it, if we still have [supplies from] Dongjiang. But [supplies from] Dongjiang is not indefinite and everlasting. Cities like Dongguan and Shenzhen will have rising demand for water and might compete for water with us,' he said. Mr Ng said Hong Kong was entitled under a water agreement with Guangdong to receive up to 1,100 million cubic metres a year from Dongjiang, which should satisfy the city's needs for 30 to 40 years. The city last year consumed 955 million cubic metres of water, about 80 per cent of which came from Dongjiang. The seawater desalination study started in 2002. A small plant with a capacity of 240 cubic metres was built at the salt-water pumping station on the waterfront of Butterfly Estate in Tuen Mun. The seawater is firstly treated by filtering out impurities. Chemicals are then added to adjust the acidity and remove chlorine. By applying high pressure to the filtered seawater, the salt is separated by a membrane, leaving pure water through the process of reverse osmosis. A similar trial will be carried out in Ap Lei Chau next year to test how the technology works on different types of seawater. This week the Water Supplies Department awarded a $4 million contract to Black & Veatch Hong Kong to launch a total water management study. The new study will explore ways of diversifying the city's water sources, including desalination, and will also project the long-term demands for water in the Pearl River Delta region.