Desalination an option to ensure free flow of Hong Kong's water supply

I refer to the letter by Mr Gravis Cheng ("Desalination is best option in the long run", December 1). I would like to provide some information in regard to the department's views on desalination and the quality of Dongjiang water.

Climate change is an issue of worldwide concern. There is no exception in Hong Kong. Indeed, the Hong Kong Observatory has forecast that climate change will exacerbate and bring about extremely dry weather more frequently.

To better prepare Hong Kong for this situation, we need to explore new water resources which will not be affected by climate change. Amongst others, seawater desalination readily offers a viable option. Currently, the cost of seawater desalination is expected to be higher than that of Dongjiang water but with the advancement in technology, the production cost of desalinated water might drop.

We are now conducting a study on the construction of our first desalination plant, to be located in Tseung Kwan O, and will look into the details of desalination technology and the financial viability of the plant.

With regard to the quality of Dongjiang water, we have been closely monitoring the water quality around the clock at the reception point on the Hong Kong side at the Muk Wu pumping station to ensure its compliance with the required water quality standard. According to our records, there has been significant improvement in the water quality since the commissioning of a dedicated aqueduct conveying Dongjiang water from the mainland. For example, the average content of dissolved oxygen has increased from 5.3 mg/L before commissioning of the dedicated aqueduct to the current value of 8.0 mg/L, while that for five-day biochemical oxygen demand has decreased from 7.1 mg/L to less than 2.0 mg/L.

Details of the water quality monitoring results of Dongjiang water are uploaded on a half-yearly basis on our website.