How Much Water Should You Drink Per Day?
Most adults need 35 ml per kg of bodyweight per day — roughly 2.5 litres (84 oz) for a 70 kg adult. Add 500–700 ml per hour of exercise and more in hot climates. Use the calculator below for your exact number.
settings Your Parameters
lightbulb Hydration Tips
Start your morning
Drink 500ml immediately upon waking to rehydrate after sleep.
Around workouts
Add 500–750ml per hour of vigorous exercise on top of your daily target.
Eat your water
Fruits and vegetables contribute 20–30% of daily water intake.
Monitor color
Pale yellow urine indicates good hydration. Dark yellow signals dehydration.
Daily Water Target
Track your intake throughout the day. Aim to drink consistently rather than consuming large amounts at once.
Related Performance Tools
How to Use This Water Intake Calculator
The calculator uses a bodyweight-based formula adjusted for activity level and climate — a far more personalised approach than the generic "8 glasses a day" guideline. Here is what each input controls:
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1
Weight. Your baseline water need scales directly with body mass — larger bodies have more cells to hydrate and produce more metabolic waste that requires water to flush out. The standard formula is approximately 35 ml per kg of bodyweight per day at rest.
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2
Activity Level. Exercise dramatically increases fluid loss through sweat. A moderate 60-minute session can produce 0.5–1.5 L of sweat depending on intensity and individual sweat rate. The calculator adds approximately 500 ml per level of activity increase — adjust manually if you are a heavy sweater or train in heat.
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3
Climate. Heat and humidity significantly increase sweat rate even at rest. People in hot or tropical climates can lose an additional 0.5–1.5 L per day above temperate baseline, and more during outdoor activity. Select the climate that best reflects your typical environment, not just the current weather.
Your result includes water from all fluid sources — not just plain water. Coffee, tea, milk, soups, and even solid foods (fruits and vegetables are 80–95% water) all contribute to your daily intake. Adjust your plain water target accordingly if you consume significant amounts of other fluids.
Why Hydration Is Critical for Performance and Health
Water is the most abundant compound in the human body, comprising 60–70% of total body weight (higher in lean individuals, lower in those with more fat tissue). It is involved in virtually every physiological process: nutrient transport, waste elimination, temperature regulation, joint lubrication, enzymatic reactions, and oxygen delivery to cells.
From a performance perspective, even mild dehydration has measurable negative effects. A deficit of just 1–2% of body weight in fluid — achievable after 60–90 minutes of exercise without drinking — has been shown in controlled research to:
- Reduce aerobic capacity (VO2max) by 5–10%
- Impair strength output by 2–3%
- Slow reaction time and reduce cognitive focus
- Increase perceived effort (exercise feels harder at the same intensity)
- Elevate core body temperature, increasing heat stress risk
At 3–4% dehydration, performance drops are severe and heat-related illness risk rises significantly. At 5%+, medical attention is warranted. The practical takeaway: do not wait until you are thirsty to drink. Thirst is a lagging indicator — by the time it registers, you are already 1–2% dehydrated.
What Water Does in the Body
- water_dropTemperature regulation. Sweat evaporation is the body's primary cooling mechanism during exercise. Without adequate hydration, sweating is impaired and core temperature rises faster.
- water_dropNutrient transport. Blood plasma — which is ~90% water — carries glucose, oxygen, and nutrients to working muscles and organs, and removes CO₂ and metabolic waste products.
- water_dropJoint lubrication. Synovial fluid — which cushions and lubricates joints — is largely water-based. Chronic dehydration contributes to joint stiffness and can worsen inflammatory conditions.
- water_dropKidney function. The kidneys filter approximately 180 L of fluid per day, concentrating waste into urine. Chronic low fluid intake raises urine concentration and significantly increases kidney stone risk.
- water_dropCognitive performance. The brain is approximately 75% water. Research from the University of East London found that dehydration equivalent to the loss of one cup of water reduced focus, short-term memory, and decision-making speed in healthy adults.
Signs of Dehydration — Early to Severe
Dehydration exists on a spectrum. The earliest signs are subtle and often misattributed to other causes — which is why so many people walk around chronically mildly dehydrated without realising it.
Mild (1–2%)
- Thirst (first signal)
- Slightly darker urine (pale yellow is ideal)
- Mild fatigue or mental fog
- Reduced appetite or increased cravings
- Slight headache
- Mild reduction in exercise performance
Moderate (3–5%)
- Dark yellow to amber urine
- Pronounced headache
- Dizziness, especially on standing
- Dry mouth and lips
- Muscle cramps
- Significant performance drop
- Constipation
Severe (6%+)
- Very dark or no urine output
- Rapid heartbeat
- Sunken eyes
- Confusion, disorientation
- Low blood pressure
- Inability to exercise safely
- Seek medical attention immediately
The Urine Colour Test
The simplest real-time hydration check is urine colour. Aim for pale straw (very light yellow). Clear urine can indicate overhydration (particularly around intense exercise with electrolyte dilution risk). Dark yellow to amber signals dehydration and the need for more fluid.
Practical Strategies to Hit Your Daily Water Target
Knowing your target is step one. Consistently hitting it is the challenge. These evidence-backed strategies make adequate hydration low-effort and sustainable:
Front-load your intake
Drink 500 ml (two large glasses) within the first 30 minutes of waking. You lose fluid overnight through breathing and minor sweating, and rehydrating first thing resets the deficit before the day begins. It also jumpstarts kidney function and can reduce morning brain fog. Use our tracker widget above to log this immediately.
Anchor drinking to habits
Pair water intake with existing daily events: a glass before every meal (3 meals = 750 ml), one before each training session, one post-workout, and one before bed. Habit-stacking removes the need to remember to drink throughout the day — you build it into your existing routine automatically.
Use a marked bottle
A 1 L bottle with time markers (e.g., "500 ml by noon, finished by 3 pm") removes all guesswork. You need to drain it roughly twice to hit most people's targets. Keeping it on your desk or in view increases consumption significantly — out of sight, out of mind applies strongly to hydration habits.
Hydrate around training
The American College of Sports Medicine recommends: 400–600 ml in the 2 hours before exercise, 150–250 ml every 15–20 minutes during moderate training, and 450–675 ml per 0.5 kg of body weight lost after exercise (weigh yourself pre and post for precision). For sessions under 60 minutes at moderate intensity, plain water is sufficient. Longer or higher-intensity sessions benefit from an electrolyte drink.
Include electrolytes for long sessions
Sweat is not just water — it contains sodium, potassium, magnesium, and chloride. During sessions exceeding 90 minutes, especially in heat, replacing only water without electrolytes can dilute blood sodium (hyponatremia), which causes nausea, cramping, and in extreme cases can be dangerous. An electrolyte tablet or drink containing 300–700 mg sodium per hour is appropriate for these conditions.
Count fluids from food
Approximately 20% of daily fluid intake comes from solid food for people eating a typical Western diet — this rises to 30–35% for those eating diets rich in fruits, vegetables, and soups. Cucumber is 96% water, watermelon 92%, strawberries 91%, and broccoli 89%. A diet rich in these foods provides meaningful fluid contribution and does count toward your daily target.
Can You Drink Too Much Water?
Yes — though it is far less common than dehydration. Drinking very large volumes of water in a short period can dilute blood sodium below safe levels, a condition called hyponatremia (literally "low sodium in blood"). Symptoms include nausea, headache, confusion, seizures, and in severe cases, brain swelling and death.
Hyponatremia risk is highest among endurance athletes who drink excessive plain water during events lasting more than 3–4 hours (marathons, triathlons, ultramarathons), and occasionally in people attempting extreme "water fasts." It is exceedingly rare in everyday, non-athletic contexts where thirst governs drinking behaviour.
The practical guidance: drink to your personalised target, not to excess. Spread intake throughout the day rather than consuming large boluses at once. During long endurance events, use electrolyte-containing drinks rather than plain water, and consider your sweat rate and race duration when planning fluid strategy.
Daily Fluid Intake Reference
Source: EFSA European Hydration Reference Values. Includes all fluid sources — not just plain water.
Hydration Questions
Most adults need about 35 ml per kg of bodyweight at baseline — roughly 2.5 L for a 70 kg adult. Add 500-700 ml for every hour of intense exercise, and more in hot or humid environments.
Yes. Despite a mild diuretic effect from caffeine, the net hydration from coffee and tea is positive and counts toward your daily fluid intake.
Yes. Drinking very large volumes in a short window can dilute blood sodium and cause hyponatremia, which is dangerous. Spread intake across the day rather than chugging.
Add roughly 500-700 ml of fluid per hour of moderate-to-intense training. Heavy sweaters or athletes in hot climates may need 1 L+ per hour plus electrolytes.
Dark yellow urine, fatigue, headache, dizziness, dry mouth, and reduced training performance are early signs. By the time you feel thirsty you are already mildly dehydrated.
It is a rough guideline, not science. A bodyweight-based target (35 ml/kg) adjusted for activity and climate gives a far more accurate intake recommendation.