"We are going to have a big flush every Monday to push all the waste that would have accumulated during the water rationing," Thaba Moyo, mayor of Bulawayo, told Agence France-Presse.
"It means everybody has to flush their toilet at the stipulated time which will be 7.30pm. This is done to prevent any sewer blockages as we anticipate longer periods without water" in the sewer system, he said.
He said residents could also flush their toilets at other times of day.
Bulawayo's chronic water shortages force the city authorities to order rationing, which reduces the amount of water getting into the sewer system.
Currently the city rations water for 72 hours each week.
Moyo said Bulawayo's chief engineer suggested the simultaneous flush.
"We are urging residents to bear with us as this is nobody's fault," Moyo said.
"It's a national problem. Most cities are having water shortages, and we are hoping that the supplies will last until the rainy season and pray that we have good rains."
Poor hygiene and sanitation have caused numerous disease outbreaks in Zimbabwe in recent years.
The problem is especially acute in suburbs, some of which go for weeks without running water as cities battle to maintain services.
Last October, more than 6 000 cases of diarrhoea were reported in the southern towns of Masvingo and Kadoma, with children the worst affected.
Four years ago more than 4 000 people died of cholera during an outbreak that affected nearly 100 000 people. – AFP