BRAZIL has the world’s biggest reserves of fresh water. That most of it sits in the sparsely populated Amazon has not historically stopped Brazilians in the drier, more populous south taking it for granted. No longer. Landlords in São Paulo, who are wont to hose down pavements with gallons of potable water, have taken to using brooms instead. Notices in lifts and on the metro implore paulistanos to take shorter showers and re-use coffee mugs.

São Paulo state, home to one-fifth of Brazil’s population and one-third of its economic activity, is suffering the worst drought since records began in 1930. Pitiful rainfall and high rates of evaporation in scorching heat have caused the volume of water stored in the Cantareira system of reservoirs, which supplies 10m people, to dip below 12% of capacity. This time last year, at the end of what is nominally the wet season, it stood at 64%.

On April 21st the governor, Geraldo Alckmin, warned that from May consumers will be fined for increasing their water use. Those who cut consumption are already rewarded with discounts on their bills. The city will tap three basins supplying other parts of the state, but since these reservoirs have also been hit by drought and supply hydropower plants, fears of blackouts are rising.

Without a downpour, Sabesp, the state water utility, expects Cantareira’s levels to sink beneath the pipes which link reservoirs to consumers a week after São Paulo hosts the opening game of the football World Cup on June 12th. To tide the city over until rains resume in November, it is installing kit to pump half of the 400 billion litres of reserves beneath the pipes, at a cost of 80m reais ($36m). The company says this “dead volume”, never before used, is perfectly treatable. Some experts have expressed concerns about its quality.

Mr Alckmin has not ruled out tightening the spigots. Flow from taps in parts of São Paulo has already become a trickle, for which Sabesp blames maintenance work. Widespread cuts could hurt the governor’s re-election bid in October. Hours after he announced the latest measures, a thirsty mob set fire to a bus.

Paulistanos use more water than most Brazilians, but lose less of it to leaks: 35%, compared with a national average of 39%. Sabesp, listed on the New York Stock Exchange but majority-owned by the state government, is a paragon of good governance, says John Briscoe, a water expert at Harvard and a former head of the World Bank mission in Brazil.

The problem exposed by the drought is that supply has not kept pace with the rising urban population. Facing a jumble of overlapping municipal, state and federal regulations, investment in storage, distribution and treatment has lagged behind. And not just in São Paulo; the national water regulator has warned that 16 projects in the ten biggest cities must be completed by 2015 to prevent chronic water shortages over the next decade. So far only five are finished; work on some has not begun. Short-term measures should keep the water trickling for now. But the well of temporary solutions will eventually run dry.