"Reasons include climate change, forest destruction, low rainfall and the operation of hydropower plants in the Vu Gia-Thu Bon river system covering Quang Nam and Da Nang," said Nguyen Truong Anh, director of Da Nang Water Supply company (DAWACO).

Meanwhile, Song Bung 4, A Vuong, Dak Mi 4 and Song Tranh 2 hydropower plants lacked water and An Trach dam had to close its discharge gates as the water level fell.

While the management of A Vuong hydropower plant has been working at a capacity of 60 cubic metres per second since early this month, the salinity level in Cau Do failed to decline.

"We cannot use water from Cau Do because of high salinity, while the water level at the An Trach dam is only 1.8-2m," Anh said. "So we have to operate a pumping system periodically in seven districts. But even then, some areas in the city will be out of water."

Residents should reserve water in tanks or buckets, he warned.

Salinity is a problem for Cau Do every year during the drought season, according to a DAWACO report. However, the situation has been getting worse.

In 2012, when salinity levels were high for 94 days, the pumping system at An Trach dam pumped 9 million cubic metres to deal with the problem.

However, last year DAWACO had to pump 23.4 million cubic metres as the high salinity level lasted for 185 days.

In the first six months this year, the company took 5.8 million cubic metres from An Trach dam to reduce salinity at Cau Do.