Water, Water Everywhere?

Lots of 'medical' advice recommends that people drink eight glasses (2 litres) of water each day. Nobody is precisely sure where this advice originated. Purveyors of overhyped and overpriced bottled water are unlikely to be unhappy at this 'directive'. Two litres of water per day may, however, actually be excessive for some folk (https://www.theguardian.com/lifeandstyle/2022/nov/24/eight-glasses-of-water-a-day-excessive-for-most-people-study-suggests?amp). A recent study in Science used more than 5,500 subjects. Living in 23 countries, subjects were between 8 days and 96 years of age. Individuals in the trial were given deuterium (a harmless radioisotope of hydrogen)-labelled water to drink. The presence of the isotope enabled the rate of the body's turnover of water to be precisely determined. Water turnover turned out to be highly variable. Some folk needed only between 1.5 and 1.8 litres per day. Drinking excess water is a waste for these people. Many people get a relatively high proportion of their water from the food they eat, reducing the need to also 'down' glasses of water! People with high energy expenditure do, however, need to drink more water. The study suggested that a wide range of water intakes could be healthy. One size does not fit all. I must admit something of a bias. My children always tell me I drink too little water. I have never, however, inspite of running ocassional marathons in hot climates, suffered from dehydration. I have also found it weird that some students feel they can't attend a one hour lecture, without bringing a bottle of water with them! I'm not anti-water (about 85% of my body mass) but everything in moderation surely?