Farmers in East Anglia have said the recent hot and dry weather has made their work "challenging".
The UK is experiencing a heatwave, and some parts of Suffolk have not seen rain for 30 days.
Tim Curry, a farmer from near Thetford in Norfolk, said his land has seen about three quarters of an inch of rain since the beginning of May.
He said they are not in "crisis" because it is still mid-season, but they would welcome rain soon.
Andrew Williams, who manages a farm at Nacton near Ipswich growing crops including potatoes, onions and broccoli, said two of the small reservoirs they use have run dry.
"It's hard work at the moment," he said.
"It's five weeks since we had any reasonable amount of rain and the irrigators have been hard at it, and they have coincided with our busiest time of year watering vegetables.
"We've invested very heavily but there's always a limit to what you can do. This is probably the most testing year in my 21 years at Nacton."
Mr Curry added that while this sort of weather is expected every few years farmers "have been slightly lulled into a false sense of security" because recent summers were "relatively benign, relatively wet and not scorching hot".
Mark Lunn, from Essex and Suffolk Water, said demand for water was 25% higher than expected - mostly from domestic customers - and urged people to "use water wisely".
Cereals farmer Robert Raven from near Beccles in Suffolk said they were "irrigating as hard as we can with the resources".
He said: "I don't think we'll see any complete crop failures because up until the end of May we actually had reasonable amounts of rain so lots of crops were quite mature by then - it's just that they won't fulfil the potential we would like them to."