Watch Claire Manning's report
The founder of Riverford veg boxes says water firms need to do more to prepare for hotter, drier summers to protect farmers.
Guy Singh-Watson, who set up Riverford Organic Farmers, says the hot weather has cost his farm tens of thousands of pounds in profit this year.
For only the second time in 36 years, one reservoir on the farm has completely dried up.
With scientists predicting climate change will bring longer, hotter summers to the UK, Guy is now planning to build a new reservoir on his farm.
He told ITV News West Country that South West Water now needs to do the same.
"The water industry was privatised in 1989 - and there has not been a reservoir built in the UK since 1991," he said.
"That's 33 years of no investment. It is extraordinary - more reservoirs were built in World War Two than have been built in 33 years of private ownership."
The lack of water means Guy has had to decide which crops to water and which ones to leave to die.
He said: "It tends to be the highest value, shallowest rooting crops [that get the water].
"We hope that the other crops will make it on their own, but they haven't."
Cabbages are one of the crops to miss out on the water - meaning the farm has lost between £20,000 and £30,000 in profit from one field alone.
Months of rain is now needed to replenish supplies.
Guy said: "A more resilient water infrastructure needs to be put in place as we look to a hotter drier future."
In a statement, South West Water said: "Through our investment and resilience planning, we have increased the amount of water the region can store, doubling it since the drought of 1976.
"We have invested in three new reservoirs as part of our ongoing water resources plans since 2007."