It would cost HK$50 billion to build a desalination plant if Hong Kong wanted its own drinking water supply, the environment minister told legislators yesterday. The estimate was unveiled as part of a feasibility study into desalination to be ready later this year. Secretary for Environment, Transport and Works Sarah Liao Sau-tung said it was too early to decide if the technology would be adopted. Trials showed desalted water would cost up to HK$8.4 per cubic metre, nearly double the cost of importing water from the Dongjiang, or East River. Hong Kong now gets between 70 to 80 per cent of its water comes from the mainland, with the rest met by local rain catchment areas. Responding to legislators' queries, Dr Liao said every city should be prepared for possible water shortages and look at alternative sources. 'No one can tell what will happen to clean water sources in the decades to come and it is the duty of each city to look at its back-up supply,' she said. Trials in Tuen Mun found capital costs accounted for half of desalination expenditure, while electricity accounted for 20 per cent. Another trial in Ap Lei Chau ends in the middle of this year. Pointing out that desalination was one of the most expensive water sources, Dr Liao said a complete replacement of Dongjiang water might cost HK$50 billion in capital costs. Wastewater recycling was equally expensive, while expanding reservoirs and catchment areas was not feasible. Dr Liao said officials would study the possibility of applying solar energy to drive the desalination process or making use of residual heat generated from power plants in an effort to minimise energy costs. The Water Supplies Department would come up with suggestions on how future water needs could be satisfied by the end of the year.