The Tanzanian authorities began rationing water in the economic capital Dar es Salaam on Thursday after water levels dropped as its main source, the Ruvu River, dried up.
The Indian Ocean city's 5.5 million residents will be deprived of running water for 24 hours on alternate days, the Dar es Salaam Water and Sanitation Authority (DAWASA) said.
"The schedule will be updated weekly depending on how the change in weather will increase or decrease water levels," DAWASA added.
Tanzania, like its East African neighbours, is experiencing little rainfall, with meteorologists warning that the prolonged dry spell will continue.
Water supply from the Ruvu River has dropped from 466 million litres a day to about 300 million litres a day, according to water officials, while the city consumes about 500 million litres a day.
"We are all aware that most areas experienced poor rains last season and the current season has been delayed," Dar es Salaam governor Amos Makalla said recently.
"Everyone should understand that this is beyond the control of the government," he added.
Four failing rainy seasons since late 2020 have caused the worst drought in at least 40 years, killing millions of livestock, destroying crops and plunging parts of Kenya, Somalia and Ethiopia - Tanzania's neighbours - into near-starvation conditions.