President Nicolas Maduro had already given most of Venezuela's 2.8 million state employees Fridays off during April and May to cut down on electricity consumption.
"From tomorrow, for at least two weeks, we are going to have Wednesdays, Thursdays and Fridays as non-working days for the public sector," Maduro said on his weekly television program.
Drought has reduced water levels at Venezuela's main dam and hydroelectric plant in Guri to near-critical levels. The dam provides for about two-thirds of the nation's energy needs.
Water shortages and electricity cuts have added to the hardships of Venezuela's 30 million people, already enduring a brutal recession, shortages of basics from milk to medicines, soaring prices, and long lines at shops.
Maduro, 53, who succeeded the late Hugo Chavez in 2013 and is facing an opposition push to remove him through a recall referendum, appealed for understanding and support.
"The Guri has virtually become a desert. With all these measures, we are going to save it," he said, adding that the daily drop in water level had slowed to 10 centimeters from 20.
After months of unscheduled outages, the government began programmed electricity rationing this week across most of Venezuela, except the capital Caracas, prompting sporadic protests in some cities.
Maduro has also changed the clocks so there is half an hour more daylight in the evening, urged women to reduce use of appliances like hairdryers, and ordered malls to provide their own generators.
Regarding the public sector measure, the government is excluding workers in sensitive sectors such as food.
Full salaries will still be paid despite the two-day week.
Critics have derided Maduro for giving state employees days off, arguing it would hurt national productivity and was unlikely to save electricity because people would simply go home and turn on appliances there instead.
"Maduro says that 'we in government don't stop working for a second'. Of course. Except for Wednesdays, Thursdays, Fridays, Saturdays and Sundays!" satirized Leonardo Padron, a columnist for pro-opposition El Nacional newspaper, via Twitter.
Officials said the El Nino weather phenomenon is responsible for Venezuela's electricity woes. But critics accuse the government of inadequate investment, corruption, inefficiency and failure to diversify energy sources.