the required fluid intake (from all sources) is more accurately 30 mls per kg of body weight. The body requires this amount of water to carry out the numerous physiological processes eg kidney function, digestive processes etc. This requirement was around when I did my training in the 1980's. So an 70kg person will need 2.1 litres whereas someone who's 100kg will need 3 litres. These requirements are what hospitals use to calculate how much IV fluid to give patients to maintain adequate hydration. I'm interested to read comments like "my husband never drinks water but is alive and mentally very active" My parents, especially my mother, often throw this type of comment at me when I remind them to drink more. "How have we managed all these years without you telling us to drink water?" and "We're still alive aren't we?" Yes, they've managed and are alive but my mother is very forgetful and gets very mixed up about things and then argues. She also has moderate osteoporosis, mainly due to inactivity and poor diet ie not enough protein and calcium and way too much processed food that's fairly low in nutrients and high in fat, sugar and salt. She also has Irritable bowel and diverticular disease and gastric reflux and washes all her mouthfuls of food down with tea, which interestingly has tannin in which prevents the absorbtion of nutrients. I was always told to chew my food and not to wash it down with drinks and we never had tea during meals when I was at home. She's also had 3 UTI's in the last 3 years, one of which caused an acute confusional state (delirium) where she couldn't remember where she was, what was happening and kept asking the same questions over and over again. Thankfully , my 18 yr old son was there at the time and recognised something wasn't right as my Dad was pretty oblivious to it all. This delirium has had a lasting effect(which is fairly well known effect) and her memory and cognition never fully returned to normal. She had a hip replacement in January and got into the habit of drinking 3 500 ml bottles of water a day. I bought the bottles of water specifically so she and I could monitor her intake. Mentally, despite having had major surgery and a stay in hospital, she was quite good regarding taking pain med's and doing her exercises etc. After about 2 months she reverted to the "plastic glass method" which involves a glass that lives in the kitchen and gets filled up in the morning and then, apparently, water is drunk out of it and each time she has a drink she tops it up. Bearing in mind that Mum spends maybe 6 hours a day sitting in front of the TV I hardly think her fluid intake is adequate. My dad also has the same attitude to drinking and is often "like a man off" in the afternoons and can't follow conversations and looks dehydrated. 3 weeks ago he fell down 3 steps at the front door at 10.30 at night and fractured his hip and tore 3 tendons in his shoulder. Even in hospital now he's very reluctant to drink enough. At the beginning that was partly because his pain was very poorly controlled and he was reluctant to walk to the loo. The ward is absolutely roasting hot but obviously he doesn't feel thirsty as long as he gets his 5 100ml cups of tea a day. He's got a chest infection now and is having problems expectorating because the secretions are so thick because he's dehydrated. They also suspect he may have a DVT (blood clot) in his leg which would certainly be due to a combination of dehydration and immobility. Think on!