Almost everyone has heard that you should drink eight glasses of water a day. The real advice is a bit looser, and a bit kinder. The UK government's Eatwell Guide, which the NHS follows, says to aim for 6 to 8 cups or glasses of fluid a day. In Europe, the European Food Safety Authority (EFSA) gives a figure for total water: 2.0 litres a day for women and 2.5 litres for men. That total includes everything: drinks, and the water that is already inside your food.
Plain water counts, but so do lower-fat milk, tea, coffee and other lower-sugar drinks, according to the NHS. Food counts too. Fruit, vegetables, soup, yoghurt and cooked grains are mostly water, and sources put the food share at roughly a fifth to a third of the total. So you do not need to reach 2 litres from the tap.
Sugary drinks are the exception to "any drink will do". They add calories without much else, and the NHS suggests keeping fruit juice and smoothies to one small glass (150 ml) a day, ideally with a meal.
Pick the figure that applies to you, then slide in a typical day. Each glass or cup here is 250 ml. The food setting is a rough guess, because nobody weighs the water in their dinner.
Thirst and pale urine are better guides than a number. Aim for the figure on most days, not every day.
The NHS says most people should drink enough during the day for their urine to be a clear, pale yellow. Dark yellow, strong-smelling urine, or peeing less often than usual, can be signs you need more. Other signs of dehydration include thirst, headache, dizziness, tiredness and a dry mouth. Some vitamin supplements can colour urine bright yellow, so the colour check is a rough guide only.
The NHS notes that you may need more fluid if you are pregnant or breastfeeding, in hot weather, active for long periods, or ill with a fever, vomiting or diarrhoea. Babies, children and older adults are more at risk of dehydration, and so are people who rely on others to get their drinks. If you take medicines that affect fluid, such as water tablets, or have a heart or kidney condition, ask your doctor how much to drink, because for some people too much fluid is the risk.
This guide is general information, not medical advice. If you have a condition, are pregnant or breastfeeding, have or have had an eating disorder, or take medication, especially for blood pressure or diabetes, talk to a doctor or dietitian about how much to drink. Seek urgent help if you feel confused, very drowsy, or are not passing urine.