In recent years, the advice to drink eight glasses of water a day has become ubiquitous, with many people carrying reusable bottles and sipping throughout the day. However, experts now warn that this obsession with hydration may be leading to excessive water intake, which can be harmful.
The so-called '8x8 rule'—drinking eight 240ml glasses of water daily—is not backed by scientific evidence. Neither UK nor EU official guidelines recommend this amount. The misconception appears to stem from misinterpretations of two older pieces of guidance: a 1945 US recommendation to consume one millilitre of liquid per calorie of food, and a 1974 book suggesting six to eight glasses of water a day, including water from food and other drinks.
Current research indicates that the body's hydration needs are highly individual and depend on factors such as temperature, activity level, and altitude. Most people require between 1.5 and 1.8 litres of water per day, not the two litres often promoted. Athletes, pregnant women, and those in hot climates may need more, but for the average person, drinking when thirsty is sufficient.
Overhydration can lead to hyponatremia, a condition where sodium levels in the blood become dangerously low, causing symptoms like nausea, headache, and in severe cases, seizures or coma. While rare, it is a risk for those who force themselves to drink large volumes of water.
Experts emphasise that the body has sophisticated mechanisms to regulate hydration. The brain triggers thirst when needed, and the kidneys adjust urine concentration to conserve water. Therefore, listening to your body's signals is more effective than adhering to rigid rules.
