Hong Kong could face water shortages within a decade because of pollution of the mainland source of much of its supply, the environment minister warned yesterday. Secretary for Environment, Transport and Works Dr Sarah Liao Sau-tung said the problem could hit even sooner if nothing was done. 'The water shortage problem will hit us in 10 years' time if Guangdong develops at the rate it is developing now,' she said. 'Although we pay for the Dongjiang water and it comes from upstream, pollution moves up at the rate of about 100 metres every year. The Dongjiang is not that long. One day it will reach the head and then what will we do?' Dr Liao's warning came days after Guangdong announced a 44.5 billion yuan (HK$41.83 billion) cleanup plan for the Pearl River and its tributaries. Guangdong is worried that economic development will ultimately be affected if water pollution cannot be controlled. It was reported that water shortages forced some Shenzhen factories to close temporarily in July. Dr Liao said Hong Kong was exploring ways to recycle water, including diverting treated waste water for non-drinking purposes. 'Waste water is no longer waste water once you treat it. It is good water that we need to conserve and use properly,' she told a Hong Kong General Chamber of Commerce/Business Coalition on the Environment lunch. A trial scheme would be carried out at the proposed Ngong Ping sewage treatment plant on Lantau, which will provide treated water to the MTR Corporation for irrigation, car washing, flushing and landscaping. But Dr Liao did not say if Hong Kong would follow the Singapore example of turning waste water into drinking water. She also called on the public not to waste water, for which the government provided a 50 per cent subsidy. The public had to be educated to conserve water, while the polluter-pays principle should be enforced to make conservation projects sustainable. Hong Kong bought about 790 million cubic metres of water from Dongjiang last year for $2.45 billion under a bilateral agreement with Guangdong. Dongjiang water accounts for about 85 per cent of the 924 million cubic metres of water consumed in the SAR. Part of Hong Kong's water payment will go to upstream Dongjiang cities to compensate them for forfeiting development along the river. But talks on price and supply beyond 2004 are still deadlocked despite three years of negotiation. The Water Supplies Department has projected that fresh-water demand will increase to 1.05 billion cubic metres by 2021. To ease the over-reliance on Dongjiang water, the department issued a document on long-term fresh water resources, estimating the varying costs of new sources. It was estimated Dongjiang water costs about $4.50 per cubic metre, versus $5.30 to recycle effluent, $7.70 for desalination and $9.10 if the reservoir catchment area is expanded. The department said it had cut consumption by at least 17 per cent by using sea water for toilet flushing. To improve Dongjiang water quality, an 80km closed aquaduct, half financed by a Hong Kong interest-free loan, is being built to transfer water to Hong Kong. It is expected that half of the pipes could be in use early next year. Conservancy Association president Albert Lai Kwong-tak said a regional assessment of long-term water demand and supply should be conducted to derive a better strategy to conserve resources. 'Guangzhou gets its own assessment, Shenzhen has one and Hong Kong also works on its own. But we don't know the whole picture,' he said.