The governor of the Brazilian state of Sao Paulo has asked for emergency clearance to siphon the remaining water out of the main reservoir serving Sao Paulo city, which has almost run dry.
After nine months of unprecedented drought, 95% of the water has gone.
Geraldo Alckmin, re-elected in last week's elections, has been criticised for not imposing water rationing to tackle the crisis.
Twenty-nine other Brazilian cities have been affected by the drought.
In Sao Paulo's main reservoir, the Cantareira system, the fall in the level has exposed a cracked earth landscape littered with the wrecks of dozens of old cars dumped over the years.
The drought has also affected other states. Rio de Janeiro and Minas Gerais are locked in an increasingly hostile battle over water resources, since Sao Paulo - the economic power engine of Brazil - is trying to draw water from a river system that also serves these other two states.
So far the crisis in Sao Paulo city has been managed by a policy of cutting water pressure at night and giving incentives to people who cut back on use.