England got just over a third of normal April rain, while Shoeburyness recorded 0.6mm and parts of Cambridgeshire and Bedfordshire saw under 5% of average.
The Environment Agency said river flows are falling at most sites, and farmers in East Anglia have begun irrigating about two weeks early, warning crop yields could drop sharply without rain.
Water supplies remain broadly normal after wetter winter weather, but Southern Water says the south-east is officially water-stressed; Scotland and Northern Ireland were wetter than average, and early May may bring showers.
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