By Barbara Plett
BBC News, Islamabad
Pakistan's Prime Minister Shaukat Aziz has appealed to the nation to pray for rain as weather officials predict a possible drought.
Many have tried to escape the punishing heat in rivers and canals
The fears follow a dry winter and no significant rains in the forecast.
Summer has only just arrived, but already people are struggling to cope. In some places, temperatures have reached 48C and water is scarce.
At least 25 people have died in a sweltering heat wave in recent days, reports quoting health officials say.
Pakistan relies on snow and winter rains from the northern mountains to fill its rivers and reservoirs before the monsoon season begins in July.
But it was an unusually dry winter and weather officials say there is not much chance of significant rain in the next two months.
Mr Aziz warned that the country is facing an intense water crisis.
Already, there are moderate drought conditions in the southern provinces of Baluchistan and Sindh.
That could affect at least one million people by the end of June.
Observers have warned that water shortages could deal a blow to Pakistan's economy, making it difficult to irrigate key crops like cotton and rice.
Newspaper editorials have also suggested that an extended drought could aggravate political problems.
There are tensions between the provinces and the central government on a number of issues.
There are also low-intensity conflicts between rebels and the state in two parts of the country - in Baluchistan and the tribal areas along the Afghan border.