Dual water supply in Hong Kong

Not many coastal cities in the world use dual water supply systems (fresh/sea water systems in two separate distribution networks) for potable and non-potable (e.g. toilet flushing, fire fighting, etc.) uses, although these are currently being operated satisfactorily in several locations world-wide (DFID, 1997). A study on the effectiveness of using seawater for non-potable purpose and how the consumption of potable water can be reduced was carried out four years ago (Smith, Stear and Parr, 1996). Its conclusion was that dual water supply systems could become an increasingly viable option for large urban areas in coastal zones. Hong Kong is one of those few cities using the dual systems, and the systems have been available since the 1950’s. The objectives of this paper are to describe the implementation of the dual water supply systems in Hong Kong and evaluate the effectiveness of the systems. Since the used water will enter the wastewater sewerage system, therefore the effect of the mixed wastewater (fresh/salt) treatment in biological sewage treatment works will also be addressed.