How Much Water Per Day Do You Really Need?

Water is often sold as the ultimate detox, and some advice makes it sound as if more is always better. In reality, your body is good at keeping its water balance, and the right amount for you depends on your size, how active you are and the weather.

This guide brings together what the NHS, Mayo Clinic and the European Food Safety Authority actually advise, what drinks count, when you need more, the signs that you are not getting enough, and why drinking far too much can also cause harm.

The short answer

The NHS suggests six to eight cups or glasses of fluid a day as a general guide. The European Food Safety Authority considers a daily water intake of 2.0 liters (about 8 cups) adequate for women and 2.5 liters (about 10 cups) for men.

Mayo Clinic gives a wider range of about 2.7 to 3.7 liters (11.5 to 15.5 cups) of total fluid a day for an average healthy adult. That range covers water from all sources, and food supplies about 20 percent of it. Fruits and vegetables such as watermelon, strawberries, cabbage and squash are almost all water.

So the figures differ a little from one health body to another. Treat them as a starting point, not a strict target.

What counts toward your total

Water is the simplest choice, but it is not the only one. The NHS says lower-fat milk and lower-sugar drinks, including tea and coffee, all count. Mayo Clinic agrees that tea, coffee and milk help you stay hydrated.

Juices, sodas and sports drinks are also options, but Mayo Clinic warns to watch their sugar, salt and calories. The NHS suggests keeping fruit juice and smoothies to one small glass of 150 ml (about 2/3 cup) a day, with a meal. It recommends swapping sugary drinks for diet, sugar-free or no-added-sugar versions, and for children, avoiding sugary fizzy drinks and juice drinks altogether.

When you need more

You may need more fluid if you are pregnant or breastfeeding, in hot or humid weather, at high altitude, active for long periods or sweating heavily. Drink extra before, during and after exercise.

Illness also raises your needs. Vomiting, fever and diarrhea all cause fluid loss, and Mayo Clinic notes that bladder infections and urinary tract stones can increase how much you need. When you are unwell, water is the best way to replace fluids, and a pharmacist can suggest oral rehydration solutions to replace lost salts if you have sickness or diarrhea.

What the evidence says

The eight-glasses rule is easy to remember and a reasonable goal, but Mayo Clinic notes that some people need less and others more. Two simple checks are more useful than any number: you rarely feel thirsty, and your urine is pale yellow or colorless.

Signs that you are not drinking enough include thirst, a dry mouth, headache, dizziness, tiredness, peeing less often and dark, strong-smelling urine. Babies, young children and older adults are at higher risk, as are people with diabetes and people taking diuretics, also called water tablets.

More is not always better. Drinking too much water is rare in healthy adults, but it can happen, for example in some athletes who drink large amounts before a long or intense workout. The kidneys cannot get rid of the excess fast enough, sodium levels fall, and this condition, called hyponatremia, can be life-threatening.

Questions people ask

This article is for general information only and is not medical advice. Herbs can interact with medicines and health conditions. Talk to a doctor or pharmacist before trying a herbal remedy, especially if you are pregnant, breastfeeding, giving it to a child, or taking any medication.