16 mai 2025

Hydration over 24 hours: water, herbal tea and infused water

Good hydration does not require a drink-by-the-clock programme or a “detox” water. For a healthy adult, the useful basics are to drink regularly, let thirst guide part of your intake, and drink more in hot weather, during prolonged exercise, or when fever, diarrhoea or vomiting increases fluid loss. Plain water is the simplest choice. Unsweetened herbal tea, tea, coffee and sparkling water count too. Fruit and herbs may make water easier to enjoy, but they do not give it special healing properties.

Two widely quoted targets look inconsistent because they measure different things. Swiss guidance recommends 1 to 2 litres of unsweetened drinks a day. The European Food Safety Authority (EFSA) sets an adequate total water intake of 2 litres a day for women and 2.5 litres for men under moderate conditions. EFSA’s total includes water from all drinks and the moisture in food. It does not mean that everyone should add 2 or 2.5 litres of drinks on top of a normal diet.

The short version

Requirements vary with body size, diet, temperature, altitude, activity, pregnancy, breastfeeding, age, illness and some medicines.
The Swiss target of 1 to 2 litres applies to unsweetened drinks. Soups, fruit, vegetables and other foods supply some of the remaining total water.
Pale yellow urine, normal thirst and regular urination are useful practical clues. Medicines, vitamin supplements and foods can alter urine colour.
Coffee and tea contribute to hydration. Their mild diuretic effect at ordinary amounts does not cancel the fluid they contain.
Herbal tea is primarily a drink. Evidence does not support the long list of benefits often attributed to chamomile, mint or ginger.
Too much fluid can be dangerous, particularly during endurance exercise. An athlete should not aim to gain body weight by drinking during an event.

How much fluid do you actually need?

No single volume suits every person on every day. The EFSA scientific opinion on water describes 2 and 2.5 litres as adequate intakes, not thresholds separating good hydration from dehydration. They apply to moderate ambient temperatures and moderate activity. EFSA proposes an extra 300 ml of total water during pregnancy and about 700 ml during breastfeeding. These are population references rather than personal prescriptions.

The Swiss dietary recommendations from the FSVO are easier to use at the kitchen table: drink 1 to 2 litres of unsweetened beverages, preferably tap water, mineral water, herbal tea or fruit infusion. The guidance explicitly says that coffee and black tea contribute to fluid intake, while caffeine should remain moderate.

The NHS uses six to eight cups or glasses as a general guide. It advises more fluid during pregnancy and breastfeeding, in hot surroundings, during prolonged activity, or while ill. The variation among these figures is a good reason not to treat every millilitre as a medical target.

Water in food counts

A tomato, melon or bowl of soup does not replace water through some unusual mechanism. Its moisture simply enters the body’s water balance. Someone who eats plenty of fruit, vegetables, yoghurt, soup and saucy dishes may need fewer drinks than someone eating dry, salty food. Vegetarian diets are not automatically hydrating; their actual food content is what matters.

A balanced smoothie provides fluid, but also the energy and sugars in its ingredients. Treat it as liquid food rather than the nutritional equivalent of water. The NHS advises limiting fruit juice and smoothies to one 150 ml serving a day because crushing and juicing release sugars and increase contact with teeth.

How to tell whether you are drinking enough

Thirst is useful for most healthy adults. The claim that any thirst means dehydration is already “well advanced” is an exaggeration. Still, it makes sense not to wait for intense thirst when working outdoors, exercising, or caring for an older person whose thirst response may be less reliable.

The NHS lists signs of dehydration: thirst, a dry mouth, dark and strong-smelling urine, less frequent urination, tiredness, dizziness and light-headedness. Pale yellow urine is a reasonable day-to-day check. Completely colourless urine all day is not a health goal and can mean that intake exceeds need.

Look at the pattern rather than one bathroom visit. First-morning urine is normally more concentrated. Beetroot, B vitamins, antibiotics and other medicines can change its colour. Persistent dizziness when standing, confusion, unusual drowsiness, fast breathing, a rapid heart rate or a marked reduction in urine needs prompt medical assessment. Use the local emergency number for severe symptoms.

A realistic hydration routine

A rigid schedule that orders a glass at 7 am, tea at 10 am and half a glass at 10 pm does not improve human physiology. A few reliable anchors work better.

Morning

Drink on waking if you are thirsty, or have a drink with breakfast. Cold, room-temperature and warm water hydrate equally well. Lemon water does not wake the liver or detoxify the body. Choose the temperature and flavour that make drinking comfortable.

Coffee or tea can be included. A crossover trial of 50 men who regularly drank coffee found no relevant difference between four cups of coffee and the same amount of water across several hydration measures. That small study does not show that every dose suits every person, but it does challenge the idea that each coffee needs a compensating glass of water. The CDC says up to 400 mg of caffeine a day can fit a healthy diet for most adults. During pregnancy, the NHS advises no more than 200 mg a day. Cup size, beans and brewing method make caffeine content highly variable.

At work or while studying

Keep a clean bottle nearby if you tend to forget drinks. Time markings can be reminders, but the bottle does not know what you ate or how hot the room is. Drink at breaks, with meals and when thirst appears. If plain water becomes boring, alternate it with sparkling water, chilled unsweetened herbal tea or safely prepared infused water.

Drinking with meals does not dilute gastric juices enough to impair digestion in a healthy person. There is no need to impose a one-glass limit. Nor is drinking large quantities before every meal to suppress hunger a necessary hydration practice.

Evening

Cut back on large amounts close to bedtime if they repeatedly wake you, but do not ignore genuine thirst. A caffeine-free herbal tea can be a pleasant ritual. Chamomile is not a proven insomnia treatment. New, intense and repeated nighttime thirst or urination deserves assessment instead of a home-made fluid schedule.

Which drinks count?

Still and sparkling water

Both hydrate. Carbonation can cause burping or bloating for some people. A mineral water high in sodium may be unsuitable as an everyday choice if a clinician has told you to restrict salt. Swiss tap water is a practical option without single-use packaging.

Herbal and fruit infusions

Unsweetened versions are among the drinks recommended by Swiss authorities. Their main job is to provide water with a different flavour and temperature. An infusion rarely supplies a meaningful dose of vitamins. A few lemon slices do not turn a jug into a nutritional supplement.

Health claims need more care. The US National Center for Complementary and Integrative Health review of chamomile finds insufficient reliable evidence for most promoted uses and notes that one insomnia study found no benefit. Chamomile in ordinary food and tea amounts is probably safe for most people, but it can trigger reactions in people allergic to ragweed, chrysanthemums, marigolds or daisies. Interactions with warfarin and some other medicines have been reported. Safety during pregnancy and breastfeeding remains poorly established.

Apply the same caution to other herbs. Ginger tea is not a standardised dose of ginger extract, and “natural” does not mean interaction-free. During pregnancy, with liver or kidney disease, or while taking anticoagulants, sedatives or other regular medicines, check concentrated medicinal blends with a pharmacist or doctor. Food-grade tea bags are not equivalent to essential oils, tinctures or supplements.

Coffee, black tea and green tea

These drinks contribute fluid. Caffeine may temporarily increase urine output, particularly at high doses or in someone who rarely consumes it, but moderate coffee does not automatically cause a net water loss. Sleep, palpitations, anxiety or reflux may give you a personal limit well below the general safety ceiling.

There is a separate vegetarian nutrition issue: tea and coffee taken with food can reduce absorption of non-haem iron. If your iron stores are low, moving these drinks away from meals makes more sense than excluding them for a false dehydration concern.

Juice, soft drinks, energy drinks and sports drinks

They contain water, but that does not make them equivalent to plain water. Soft drinks, sweetened iced tea, energy drinks and many “vitamin waters” add sugar or sweeteners. Energy drinks may combine several caffeine sources.

A sports drink is unnecessary for a walk, easy cycle commute or short gym session. Carbohydrate and sodium may be useful during long, hot and sweaty activity, but the right plan depends on duration, intensity and sweat losses. Read the guide to hydration and electrolytes for vegetarian athletes rather than applying one recipe to every workout.

Alcohol

Alcohol is not a hydration strategy. It can increase urinary losses, impair judgement and complicate heat or exercise recovery. Beer after exercise does not replace water or a proper recovery meal.

Preparing infused water safely

Cucumber water and strawberry water are still made with fresh produce. Soaking fruit does not disinfect it, and lemon does not sterilise the jug.

Wash your hands and start with a clean jug.
Choose produce without mould and cut away damaged areas.
Rinse fruit, herbs and vegetables under running water before cutting, including citrus peel that will sit in the drink.
Do not use soap or washing-up liquid on produce. The FDA recommends running water, gentle rubbing and a clean brush for firm produce such as cucumber.
Make a small batch and refrigerate it immediately. FDA guidance keeps perishable produce at 40°F, about 4.4°C, or below.
Pour into a glass rather than drinking from the jug. Do not keep topping an old mixture up with new water.
Discard it after a long period in the heat or if it becomes unexpectedly cloudy, fizzy or smells unusual.

For one litre, try six cucumber slices with mint; a small handful of crushed raspberries with lime; or sliced apple with a small piece of cinnamon. One or two hours in the refrigerator usually develops enough flavour. Eat fruit separately if you want its fibre and nutrients; very little moves into the water.

Cold-brewed tea and herbal infusions also need clean equipment and refrigeration. Fermented drinks are a different process, with live cultures and additional controls. Our guide to home-made kefir, kombucha and ginger beer covers those methods.

Heat, exercise and illness are different problems

During a heatwave

Drink more often, stay cool and reduce exertion during the hottest hours. Sweat loss varies widely, so no fixed extra amount is right for everyone. Older adults, young children and people who depend on someone else for access to drinks face more risk. The guide to no-cook meals and hydration during heatwaves collects practical measures for hot days.

During exercise

The familiar advice to drink 500 ml before exercise and sip every 15 minutes sounds precise but ignores body size, pace, weather and sweat rate. The National Athletic Trainers’ Association position statement recommends an individual plan that prevents both underdrinking and overdrinking. Weighing yourself before and after a comparable session can help: weight gain during exercise means fluid intake exceeded losses.

Exercise-associated hyponatraemia is a fall in blood sodium during or up to 24 hours after prolonged activity. A clinical review by Rosner identifies excessive fluid intake, often combined with reduced renal water excretion, as the central mechanism. Sodium in a sports drink does not protect an athlete who drinks too much of it. Drinking in response to thirst during endurance activity is a reasonable safeguard against overhydration. Confusion, repeated vomiting, a severe headache, seizure or altered consciousness during or after an event is a medical emergency. Do not respond by blindly giving more water.

For a fuller performance plan, see hydration for vegetarian athletes and the article on coffee in sports nutrition.

With vomiting or diarrhoea

These illnesses remove salts as well as water. The NHS advises small sips when nausea makes drinking difficult and a pharmacist-recommended oral rehydration solution when losses are substantial. The World Health Organization describes oral rehydration salts as a glucose-electrolyte solution designed to treat dehydration from diarrhoea. Infused water and standard sports drinks do not have the same formulation. Babies, young children and older adults can deteriorate more quickly.

Who should not follow a general target without advice?

A prescribed fluid restriction or target for heart failure, kidney disease, liver disease, a sodium disorder or another condition takes priority over this article. The same applies to people taking diuretics or medicines that affect water balance. Do not turn 1 to 2 litres into an obligation when your care team has given different instructions.

Persistent excessive thirst, particularly with very high urine output, needs investigation. At the other extreme, swelling, shortness of breath or rapid weight gain should not be self-treated by changing water intake. Pregnancy and breastfeeding raise average needs, but medicinal herbs and caffeine need separate consideration.

Common mistakes

Adding targets without checking their definitions. EFSA’s 2 to 2.5 litres include food moisture; the Swiss 1 to 2 litres refer to drinks.
Trying to keep urine colourless. Pale yellow is usually enough, and colour is only one clue.
Assuming coffee cancels water. Moderate coffee and tea contribute to fluid intake.
Treating every herb as medicine. The flavour is real; claims about sleep, immunity, digestion and detoxification are much less certain.
Leaving a fruit jug on a desk all day. Cut produce is perishable and belongs in the refrigerator.
Forcing large volumes in endurance events. Drinking beyond losses can cause hyponatraemia, even with sports drinks.
Using plain water alone for major diarrhoeal losses. Oral rehydration solution has a different purpose and composition.

Frequently asked questions

Must everyone drink exactly eight glasses a day?

No. Six to eight glasses is a practical NHS guide, not a biological rule. Glass size, food, temperature and activity alter the total.

Is cold water better than warm water?

Both hydrate. Choose the one you enjoy. A cool drink may feel better after exercise in heat, but no temperature detoxifies the body.

Can you drink with meals?

Yes. Water with food does not dangerously dilute digestive juices in a healthy person. Adjust the volume for comfort if you have reflux or bloating.

Can lemon water affect teeth?

Repeated acid exposure can contribute to enamel erosion. Avoid sipping strongly lemon-flavoured water for hours, do not brush immediately after an acidic drink, and use plain water as your main drink.

Does herbal tea count as water?

Yes, it contributes fluid. That does not confirm its health claims. Check the ingredients during pregnancy, with allergies or when taking medicines.

Should you add salt to a water bottle?

Not for an ordinary day or short session. Sodium can matter during long activity with heavy sweat losses, but it should be proportionate. Salt cannot prevent hyponatraemia when an athlete overdrinks.