Why the 'two litres a day' water rule is outdated and misleading

The idea that everyone should drink two litres of water a day has long been a common health claim. But experts now say this one-size-fits-all advice lacks solid scientific backing. Instead, hydration needs depend on factors like age, activity level, climate and overall health. For decades, the 'eight glasses a day' rule—roughly two litres—was widely promoted as the ideal water intake. Over the past 20 years, however, research has shifted toward more personalized recommendations. The European Food Safety Authority (EFSA) now suggests women consume 2.0 to 2.5 litres daily, while men should aim for 2.5 to 3.3 litres, including fluids from food. In the U.S., guidelines from the National Academies recommend 2.7 litres for women and 3.7 litres for men. Germany's Nutrition Society (DGE) advises around 1.5 litres from drinks alone, with additional fluids coming from meals. The kidneys of a healthy adult can process about one litre of water per hour, but individual needs vary widely. Some people may require as little as one litre a day, while others—such as athletes, pregnant women, or those in hot climates—might need up to six. Physical exertion, breastfeeding, and high temperatures all increase the body's demand for fluids. Food also plays a key role in hydration. About 30 percent of daily water intake comes from meals, especially water-rich foods like cucumbers, watermelons, and leafy greens. A balanced diet with plenty of fresh produce naturally helps maintain fluid levels, reducing the need for extra drinks. Experts also note that natural thirst is the body's most reliable signal for when to drink. While staying hydrated is important, drinking too much water can be dangerous. Overconsumption may lead to water intoxication, where sodium levels drop too low, causing symptoms ranging from headaches to life-threatening complications. Spreading fluid intake evenly throughout the day is far more effective than consuming large amounts at once. Current guidelines no longer support a fixed two-litre target for everyone. Instead, they emphasize listening to thirst cues and adjusting intake based on personal circumstances. For most adults, the German Nutrition Society recommends 30 to 40 millilitres of fluid per kilogram of body weight—including water from both drinks and food.