A turning tide that could leave Hong Kong in deep water

At a celebration to mark the semi-centenary of the Dongjiang's supply of fresh water to Hong Kong, the narrative of a commemorative video chimed soothingly: "Gently flowing for 50 years, nourishing the beautiful Pearl of the Orient."

The agreement on water supply from the river was renewed in May for another three years, and while this will make officials sleep easier, experts are less sanguine.

They worry that it is this very security of Hong Kong's water supply that makes it vulnerable to overreliance on the mainland when it should be doing more to boost alternative sources and reduce overconsumption, a serious affliction in the city.

While Chief Executive Leung Chun-ying thanked the mainland government for giving the city "top priority" in its water needs, Hong Kong should not be lulled into thinking the Dongjiang supply is its sole preserve.

"We are under the false impression that the Dongshen Water Supply Project was built for Hong Kong exclusively," says independent water researcher Su Liu, founder of a non-profit think tank, Hong Kong Water Focus.

"This was the belief in the beginning, but the project has become too important for the whole Pearl River Delta region."

Extreme weather, floods, droughts and a competitive scramble for water in southern China could occur and this could undermine Hong Kong's position downstream, she warns.