Thunderstorms brought slight relief to parts of northern Vietnam in recent days but not to the Hoa Binh hydropower plant, where water levels hover just above the "dead point" when electricity output is severely restricted.
In fast-growing Vietnam, where energy demand outstrips supply, that means further blackouts in a country that draws more than one-third of its power from hydroelectricity.
The Hoa Binh power facility is Vietnam's largest, fed by the Da River flowing from China, where drought has brought falling water levels just as it has throughout Southeast Asia.
Vietnam is confronted with its worst water shortage in decades, Bui Duc Long, of the national weather center, told AFP.
Vietnamese media reports have said the dry spell which has pushed temperatures in Hanoi to near 40 degrees Celsius (104 Fahrenheit) could be the worst in a century.
"This year the drought is worse than usual because we haven't seen the rise in levels that originate upstream in China", said Hoa Binh Hydro Power Company's deputy director Nguyen Khac Thuc.
Foreign businesspeople have expressed regular concern about a lack of energy and other infrastructure in Vietnam.
"Consumption of electricity keeps on growing by 15 percent annually, thereby substantially surpassing the economic growth rates," the European Chamber of Commerce in Vietnam wrote last month.
It cited estimates that the country needs around US$70-80 billion of infrastructure investment over the next five to 10 years.
At Hoa Binh, electricity production has already been limited for several months, initially to maintain the reservoir at its normal level of 117 meters (384 feet), said Thuc, whose plant is under the state Electricity of Vietnam (EVN) company.
After a subsequent release of water to irrigate farm fields, the level dropped in late May to 83 meters, and then to just above 81 one meter higher than the "dead point", he said.
On Wednesday afternoon, the levels were above 82.
"They went up slightly but very slowly because there hasn't been rain," he said. "We have a difficult job."
Below the dead point, production must be limited to a "strict minimum", lest the water fall to 75 meters which requires a halt in electricity output, Thuc explained.
The imposing Hoa Binh facility includes a towering statue of Vietnam's independence hero Ho Chi Minh. The plant was built over 15 years with help from the former Soviet Union and has a capacity of 1,920 megawatts.
Inaugurated in 1994, it now serves more than 40 percent of electricity consumption in northern Vietnam and 15 percent nationwide, the company says.
But it is not enough.
For the first five months of the year Vietnam had a shortage of two billion kilowatt-hours, said Quan Duc Hai, of EVN's National Load Dispatch Centre.
Vietnam's economic growth has exceeded five percent annually for the past decade. Electricity demand comes not only from industry but from increasingly well-off householders buying appliances.
Upstream from Hoa Binh, the even larger Son La hydro facility is under construction. It is designed with a capacity of 2,400 megawatts and is to be fully operating in 2012, official media said.
The electricity sector is growing more than 13 percent annually but power shortages still occur for several reasons including insufficient water during the dry season, the state Vietnam News quoted Deputy Prime Minister Nguyen Sinh Hung as telling the National Assembly.
The country is trying to diversify its energy sources, including with nuclear power. Initial government plans call for four reactors, with a total capacity of 4,000 megawatts, at least one of which should be operational from 2020.
For the moment, power cuts continue.
In northern Vietnam the rainy season traditionally begins in May. This year, the rains still have not come.