Assistant director of water supplies Bobby Ng Man-tung said the technology was able to locate leaks more accurately and quickly. He was reporting the results of a recent study trip to the United States.

Ng said the system worked like an endoscope in a pipeline, with a closed-circuit television camera or an acoustic sensor inserted into the mains through an opening about 50 millimetres in diameter. Pipeline service would not be interrupted during the process.

The system takes eight hours to cover one kilometre of pipeline, faster than the existing method with acoustic sensors, which send signals to a central processing unit.

'If the pilot scheme proves efficient, we will consider adopting the system permanently for routine inspection work,' Ng said.

The department is giving priority to inspecting leaks after a burst pipe under Gloucester Road in September caused traffic chaos and led to concern about the condition of many old pipes in busy areas.

So far, of about 500 sections of mains crossing major traffic routes, with a total length of three kilometres, 60 per cent had been completed. Inspections found 17 sections with risk of leakage, all of which had been repaired.

The department has been replacing or repairing 3,000 kilometres of pipelines since 2000. Work has been completed on 1,000 kilometres of pipelines under the 15-year programme, costing HK$21.8 billion. It covers the 18 districts in the city.

Department figures show that replacement work was proceeding the slowest in Wan Chai. But the department said adding more work to that already in progress there would disrupt traffic.

Cash flow

The 15-year programme to replace

3,000 kilometres of water pipelines will cost, in billions of HK dollars: $21.8