A leading surgeon has recommended people drink three litres of water a day and said a "radical culture change" towards drinking water is required to help the country stay hydrated during the heatwave.
Bhaskar Somani, a consultant urological surgeon at University Hospital Southampton NHS Foundation Trust, said attitudes towards water consumption "remained poor" even among those at higher risk of health problems.
He said: "We should take this opportunity to remind people that consumption of three litres of water a day is a small price to pay to help maintain and improve your health, particularly during heatwave spells such as the one we are in right now."
He spoke out following a study of 162 patients who received treatment for kidney stones - for which poor hydration is a significant risk factor - at Southampton General Hospital.
It found less than a third (28%) increased their water intake, despite receiving advice after treatment on the need to drink 2.5 to 3 litres a day, particularly in the summer months, with the average intake of water at around 1.5 litres.
Almost a quarter (22%) said the reason for avoiding water was because they didn't like the taste, while 26% blamed their habits and 10% said they only drank when thirsty.
Mr Somani said: "As a urologist, it clearly concerns me that patients who have suffered with the pain and discomfort of kidney stones are not keen to take this simple step to help improve their health.
"It then begs the question that, if those are the views of people in a high-risk group, what is the feeling among those who have no current health risks which could be aided by better hydration?"
He added: "As the country contends with this sustained period of extremely hot weather, we need to draw attention to why attitudes towards hydration remain
poor and how we can bring about a radical culture change to address it."
Mr Somani said his team had seen a rise in the number of patients admitted to hospital with renal colic - a pain associated with kidney stones - and stone formation in the past three weeks, but the effects stretched much further.
He explained: "Emergency departments are seeing large numbers of elderly patients who are dehydrated, along with outdoor workers who are battling the heat during the hottest parts of the day - and many of the problems tie in with poor fluid intake."
The NHS Choices website recommends people drink 1.2 litres of water daily (six to eight glasses) but adds: "In hotter climates, the body needs more than this. We also get some fluid from the food we eat."