Last updated: October 2026
The NHS says adults should aim for 6 to 8 glasses of fluid a day, about 1.2 to 1.6 litres if a glass holds 200ml. Water, tea, coffee and lower-fat milk all count. You need more in hot weather, when exercising or unwell, and if pregnant or breastfeeding. Pale straw-coloured pee means you’re drinking enough.
Below: the figures in litres, pints and bottles, the “8 glasses” myth, what counts, signs of dehydration, drinking too much, and what water really does for weight loss and skin.
How much water should I drink a day? The UK guidance
The NHS advice is 6 to 8 cups or glasses of fluid a day. It’s a guide rather than a strict target, and it covers all drinks, not just plain water.
The British Dietetic Association (BDA) puts numbers on it. It gives an adequate intake from drinks of about 1.6 litres a day for women and 2 litres for men, and says drinks supply around 70 to 80% of the water we need. The other 20 to 30% comes from food such as soup, stews, fruit and vegetables.
Those BDA figures line up with the European Food Safety Authority (EFSA), which sets an adequate total water intake, from food and drink together, of 2.0 litres a day for women and 2.5 litres for men. So the European “2 litres” includes the water in your meals.
Quick conversions for 6 to 8 glasses (1.2 to 1.6 litres)
| Measure | Roughly |
|---|---|
| Glasses or mugs of 200ml | 6 to 8 |
| 500ml bottles | About 2.5 to 3 |
| UK pints (568ml) | About 2 to 3 |
| BDA drinks figure for men (2 litres) | 4 bottles, or about 3.5 pints |
There is no official UK formula based on body weight. Bigger, more active people need more, so thirst and pee colour are better day-to-day guides than an app.
The 8 glasses a day myth: where it came from
“Drink at least eight glasses of water a day” is everywhere, but it isn’t UK guidance in that form. A well-known 2002 review by the US physiologist Heinz Valtin looked for the scientific evidence behind “8 x 8” (eight 8oz glasses) and found none for healthy adults in a temperate climate. He also found that caffeinated drinks can count towards the total.
The rule is often traced back to a 1945 US recommendation of about 2.5 litres of water a day. That figure included the fluid in prepared foods, a detail that seems to have been lost along the way.
Eight glasses is a reasonable amount for many people. You just don’t need 8 glasses of plain water on top of your tea, coffee and meals.
What counts towards your fluid intake
The NHS says water, lower-fat milk and lower-sugar drinks, including tea and coffee, all count. Here is how common drinks compare.
| Drink or food | Does it count? | How much |
|---|---|---|
| Tap, bottled or sparkling water | Yes, the best everyday choice | As much of your 6 to 8 glasses as you like |
| Tea and coffee | Yes | In moderation: the BDA gives 400mg caffeine a day as the safe limit for adults, and 200mg if pregnant |
| Lower-fat milk | Yes, and it stays in the body well | A glass or two a day fits most diets |
| Sugar-free squash and diet drinks | Yes | Fine as part of your total |
| Fruit juice and smoothies | Yes, but high in sugar | No more than 150ml a day in total, with a meal (NHS) |
| Sugary fizzy drinks and energy drinks | They contain water, but they’re not a good source | Keep occasional |
| Alcohol | Not a good way to hydrate | Avoid in hot weather (NHS) |
| Food (soup, fruit, vegetables, yoghurt) | Yes | About 20 to 30% of your water (BDA) |
Does coffee dehydrate you?
Only a little. The BDA says caffeine has a small dehydrating effect, but tea and coffee still help you stay hydrated. In a University of Birmingham study of 50 regular coffee drinkers, four 200ml mugs of coffee a day hydrated as well as the same amount of water. A UK trial of 13 drinks found coffee, tea, cola, sparkling water and lager produced no more urine over four hours than still water, while milk was held in the body for longer.
Caffeine has other effects, though: see does caffeine cause anxiety?, coffee on an empty stomach and are energy drinks bad for you?
When you need to drink more
The NHS says you may need more fluid if you are:
- Pregnant or breastfeeding. Keep caffeine under 200mg a day in pregnancy. We don’t recommend our products during pregnancy or breastfeeding.
- In a hot environment. In a heatwave, the NHS advises extra fluids and regular cold drinks, and avoiding alcohol, caffeine and hot drinks while trying to cool down. Saunas count too: see sauna benefits and safety.
- Physically active for long periods. Drink extra to replace sweat. After long or very sweaty sessions, see electrolytes vs water and muscle recovery.
- Ill or recovering from illness, especially with a fever, vomiting or diarrhoea. A pharmacist can recommend oral rehydration solution.
If you’ve had kidney stones, the NHS advises adults to drink 2.5 to 3 litres of water a day to help prevent them coming back. If your doctor has given you a fluid limit, for example for a heart or kidney condition, follow that instead of general advice.
Signs of dehydration and the pee colour check
The NHS lists these signs of dehydration in adults and children:
- feeling thirsty
- dark yellow, strong-smelling pee, and peeing less often than usual
- feeling dizzy or light-headed
- feeling tired
- a dry mouth, lips and tongue
- sunken eyes
- a headache
The simplest check is your pee. The BDA says pale straw-coloured urine shows you’re well hydrated, and the NHS advises drinking enough during the day that your pee stays pale.
Mild dehydration can play a part in a sluggish afternoon or a morning headache: see waking up with a headache, tension headaches, the afternoon slump and why am I always tired? After a night out, see our hangover guide.
Get help: the NHS says to get an urgent GP appointment or call 111 if you feel unusually tired, dizzy when you stand up and it doesn’t go away, have dark pee or are peeing much less, or have a fast heartbeat or fast breathing. Call 999 if someone is confused, very drowsy or hard to wake, has difficulty breathing, or has cold, blotchy, pale, blue or grey skin, lips or tongue.
Can you drink too much water?
Yes, although it’s rare in everyday life. Drinking far more than your kidneys can clear dilutes the sodium in your blood, a condition called hyponatraemia. Symptoms can include headache, nausea and vomiting, tiredness, muscle cramps and confusion, and severe cases can cause seizures.
The main risk is in long endurance events. In a study of 488 Boston Marathon runners, 13% finished with low blood sodium and 0.6% with critically low levels. The biggest risk factors were gaining weight during the race (drinking more than you sweat out), taking over 4 hours, and being very light or heavy.
On a marathon or long hike, drink when you’re thirsty rather than at every stop. Day to day, there’s no benefit in going far beyond what keeps your pee pale.
Does drinking water help you lose weight?
A little, mainly by helping you eat less. In a 12-week trial, 48 adults aged 55 to 75 followed a reduced-calorie diet, and half also drank 500ml of water before each main meal. The water group lost about 2kg more than the diet-only group. At the start of the trial, drinking water before a meal cut the meal by about 40 calories.
That’s one small study, and everyone was also eating less. The bigger win for most people is swapping sugary drinks and juice for water. See sugar cravings and how to build healthy habits that stick.
If you feel puffy or swollen, see water retention for common causes and what helps.
Does drinking more water help your skin?
The honest answer: maybe slightly, and mostly if you don’t drink much now. A 2018 systematic review found only six small studies and called the evidence weak. They showed a slight increase in skin hydration after drinking more water, mainly in people who drank little before. Whether it actually reduces dry skin is still unknown.
So the TikTok “glow” from a gallon a day is overstated. Stay well hydrated, and look after your skin from the outside with moisturiser and sun protection.
Older adults and children
Older adults
The BDA notes that thirst is not a useful guide in older adults, and the NHS says older people are at higher risk of dehydration, as well as of heat illness at 65 and over. If you care for an older relative, offer drinks regularly rather than waiting for them to ask.
Children
The NHS says the best drinks for children are water and milk, and that they should avoid sugary fizzy drinks, squash and juice drinks completely. Babies, young children and older adults are all more at risk of dehydration. Speak to a GP, health visitor or pharmacist about how much your child needs, especially if they are unwell. Our products are for adults (18+) only.
Simple ways to drink enough
- Start the day with a glass of water before your first coffee.
- Have a drink with every meal and snack. That covers much of your 6 to 8 glasses.
- Keep a refillable bottle in sight at your desk or in your bag.
- Eat water-rich food: soup, fruit, vegetables and yoghurt all count. See food and mood.
- Drink extra when you sweat, and check your pee colour.
- Ease off in the last hour before bed if you wake up to pee at night.
If you take a magnesium drink, it can be part of your evening glass. Our Magnesium Glycinate Sleep Complex is a berry-flavoured powder you stir into water, with magnesium bisglycinate and citrate plus L-theanine and chamomile. Magnesium contributes to electrolyte balance and to the reduction of tiredness and fatigue.
FAQs
Is 2 litres of water a day too much?
No, not for most healthy adults. The BDA gives about 2 litres of drinks a day for men and 1.6 litres for women, and EFSA’s totals of 2.0 litres for women and 2.5 litres for men include water from food. If your doctor has given you a fluid limit, follow that.
Do tea and coffee count towards your water intake?
Yes. The NHS says tea and coffee count towards your daily fluid. Caffeine has only a small dehydrating effect, and a study found moderate coffee hydrated as well as water.
How many 500ml bottles of water should I drink a day?
About 2.5 to 3 bottles covers the NHS 6 to 8 glasses, counting all your drinks. Men may need around 4 in total. Drink more in hot weather or when exercising.
Is sparkling water as hydrating as still water?
Yes. A UK trial comparing 13 drinks found sparkling water hydrated just as well as still water.
What colour should my pee be?
Pale straw. Dark yellow, strong-smelling pee is a sign of dehydration, so drink more until it turns pale.
Can drinking too much water be dangerous?
Rarely, yes. Drinking far more than you need, usually during long endurance events, can dilute the sodium in your blood (hyponatraemia). Drink to thirst during long events and don’t finish heavier than you started.
Sources
- NHS. Water, drinks and hydration.
- NHS. Dehydration.
- British Dietetic Association. Fluid (water and drinks) and hydration. Food Fact Sheet, 2026.
- NHS. Heatwave: how to cope in hot weather.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on dietary reference values for water. EFSA Journal 2010;8(3):1459. Summarised in Fernández-García JM et al. Hydration and natural mineral water. Semergen, 2025.
- Medical News Today. How much water should you drink a day? (1945 US Food and Nutrition Board figure).
- MedlinePlus. Low blood sodium.
- Valtin H. “Drink at least eight glasses of water a day.” Really? Am J Physiol, 2002.
- Killer SC et al. No evidence of dehydration with moderate daily coffee intake. PLoS One, 2014.
- Maughan RJ et al. A beverage hydration index. Am J Clin Nutr, 2016.
- Almond CS et al. Hyponatremia among runners in the Boston Marathon. N Engl J Med, 2005.
- Dennis EA et al. Water consumption increases weight loss during a hypocaloric diet. Obesity, 2010.
- Akdeniz M et al. Does dietary fluid intake affect skin hydration? Skin Res Technol, 2018.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex.
