By Will Grant
BBC News, Caracas
Water rationing could last for six months in some parts of Caracas
Large parts of the Venezuelan capital, Caracas, will be without water for up to 48 hours over the next week after officials began water rationing.
The measure is the start of a possible six months of rationing before the rainy season in Venezuela begins again.
Venezuelan President Hugo Chavez has said the unseasonably dry past few months have caused the water shortage.
However, his critics accuse him of failing to properly invest in water provision for the capital.
Residents awoke to dry taps as the first day of a possible six months of the measures.
More than 20 main districts of Caracas were affected with a further 24 due to have their water cut off later on Tuesday.
In most cases, people were warned of the problem ahead of time and had taken measures to stockpile water in tanks, containers and bottles.
El Nino effect
But some of the poorer parts of the city are already dependent on emergency supplies of clean drinking water, delivered every 11 days by tanker.
Mr Chavez has blamed the problem on a particularly dry rainy season, saying the climatic effect of El Nino is to blame for the city's empty reservoirs.
The socialist leader recently urged Venezuelans to take no more than three minutes in the shower to save on water and electricity.
But the opposition are unconvinced. They say the problem has been exacerbated by a chronic lack of investment in hydrology systems and aquaducts by the Chavez government.
The director of an opposition-run water institute, Norberto Bausson, told the BBC that the problems in Caracas were the result of the water delivery system not growing at the same rate as the city over the past 10 years, leading to shortages and emergency rationing.
There have been similar problems in electricity provision recently - especially in regions in the south supplied by large hydro-electric dams where blackouts have become increasingly common.