A water station in Hoang Mai District, Hanoi. Underground water throughout the country is dangerously polluted, according to the Ministry of Natural Resources and Environment.

In the capital, Tu Liem District's Mai Dich Ward has ammonia levels significantly higher than the allowed limit. In Dan Phuong District's Tan Lap Commune, the ammoniac concentration can reach 23.30mg per liter – 233 times higher than the limit. The water also contains excess manganese and arsenic.

Moreover, a report by the Vietnam Environment Administration found that coliform and phosphate in underground water exceeded the limits by hundreds and even thousands of times.

The problem is equally pervasive in HCM City, especially Binh Tan District, as well as other regions. Central Highlands is now the only region that has safe sources of subterranean water, according to experts.

The rapid development of industry and trade villages and the use of chemical fertilizer and insecticide were the main causes of pollution, said Deputy Director of the Vietnam Environment Administration Le Ke Son.

The concentrations of cyanide and NH3 in waste water produced by garment, textile, and paper industries often exceeded the recommended limit by as much as 84 times.

The management of pollution was becoming more and more difficult due to the rapid increase of factories, he said, coupled with the large-scale failure to treat waste water.

It costs much more time and money to tackle pollution of underground water than surface water, explained Tran Thi Hue, a water resources expert from the Department of Water Resources Management.

Emphasising that industrial enterprises were responsible for the pollution, she warned that the current fine of VND500 million (nearly US$24,000) was not heavy enough to deter enterprises from disposing waste into the environment.

"Underground water is being exploited in large amounts in provinces such as Hung Yen, Hai Duong and Vinh Phuc and the water source is likely to be exhausted if it is not well managed," she said.