Groundwater is receding by 0.5-1 metre a year in HCM City, Nguyen Van Nga, head of the city's Natural Resources and Water Division, has warned.

In the outlying districts of 12, Hoc Mon, and Cu Chi there will be no restrictions on digging wells and drawing water except with regard to the depth at which water can be exploited.

Speaking at a meeting in the city on Wednesday, he said the areas with the greatest decline are Districts 12, Binh Chanh, and Binh Tan where the water levels have receded to 25-34 meters below the surface.

Phan Van Tuyen of the HCM City University of Science said the depletion of groundwater is creating empty areas, causing land to sink.

Many places in Districts 6 and Binh Tan have sunk in this manner, he said.

If the problem is not mitigated promptly, it would have serious consequences on transport infrastructure and construction works, he said.

The department is creating a map to mark zones where groundwater exploitation will be reduced or even prohibited by 2020.

It has identified three such zones.

In the banned zone, straddling nine districts (1, 2, 3, 4, 5, 6, 7, 10, and 11 ) and part of the outlying Nha Be, new wells will not be allowed.

The 195-sq.km area has seen the greatest decline in groundwater levels, and faces a more serious threat of land sinkage than other places.

Tan Binh, Phu Nhuan, Go Vap, Binh Thanh, Binh Chanh, and Can Gio Districts and a part of Nha Be come under a restricted zone where the volume of water drawn will be curtailed.

In the outlying districts of 12, Hoc Mon, and Cu Chi there will be no restrictions on digging wells and drawing water except with regard to the depth at which water can be exploited.

The city has about 300,000 bore wells that exploit 670,000cu.m of water a day, according to the Division for Water Resources Planning and Investigation for southern Viet Nam.