Cornish fire crews were called out to more than four times the number of incidents on Thursday than on the same day a year ago.
Cornwall Fire and Rescue Service said they deployed crews to 135 incidents, compared to 30 in 2021.
It is asking people not to have BBQs and to take care when putting out cigarettes.
At Boardmasters organisers are bringing in additional water supplies after reports of a shortage from some people.
Temperatures are expected to pass 30C (86F) again for much of Cornwall on Friday and the government has announced Devon and Cornwall are officially in drought conditions.
Temperatures are expected to pass 30C (86F) again for much of Cornwall on Friday and the government has announced Devon and Cornwall are officially in drought conditions.
Alistair, 17, from Gloucestershire, is at Boardmasters and said there was a shortage on his campsite: “All the taps yesterday were broken for a large proportion of the day so was feeling the heat quite a lot.
“We only managed to get one big bottle of water and a couple small ones all day yesterday for the group I’m in of six.”
He said issues remained on Friday morning with taps working intermittently.
Boardmasters said in a statement: “With a hot weekend ahead, we are taking proactive measures and bringing in our own additional water tankers on site so there is plenty for our festival goers and crew, and so we do not need to rely on local water networks.
“Water remains available from our bars and free water points across the main arena and campsites. Boardmasters organisers remind customers to wear a hat, stay hydrated and wear sun cream.”
There are also warnings Bodmin Moor is at risk of further fires that could add pressure.
Rupert Hanbury-Tenison, an expert in land management, said: “It is incredibly dry. We have been doing a lot of environmental work over the past 20 years to improve bio-diversity and carbon sequestration and water retention on the moor.
“That has meant that we have a lot more vegetation and it is absolutely tinder dry. We are all holding our breath really because it’s very worrying.”
Stunning images also show the extent to which water levels have depleted at Cornwall’s largest reservoir on Bodmin Moor.
‘Exceptionally low’
Levels at Colliford Lake are now so low that trees and rocks that are usually submerged have been exposed.
The amount of water held in England’s reservoirs stood at just 65% of total capacity at the end of last month – the lowest level for that point in the calendar year since 1995, according to figures from the Environment Agency.
The agency said most reservoirs were now classed as being “exceptionally low”.
It said water levels were lowest at Colliford reservoir in Cornwall, which is only 43% full, and Stithians reservoir in Cornwall, where levels were at 44%.