Daily Water Intake & Hydration Calculator
Calculate your personalised daily water intake based on body weight, activity level, climate, and health status.
Hydration Guide
Daily Water Needs
WHO/EFSA guidelines: adult women 2.0 litres/day total fluid intake (from all sources including food). Adult men 2.5 litres/day. NHS recommendation: 6-8 glasses (approximately 1.5-2 litres of fluid per day) in a temperate climate. These are baseline figures — needs increase significantly with exercise, heat, and certain medical conditions. Approximately 20-30% of daily water needs come from food (fruit, vegetables, soups). So for a 2-litre target, approximately 1.4-1.6 litres needs to come from d
Exercise and Sweat Loss
Sweat rate varies enormously: 0.5-2 litres per hour depending on intensity, heat, and individual variation. For exercise under 60 minutes at low intensity: drinking to thirst is generally adequate. For prolonged exercise or in heat: pre-hydrate (500mL 2 hours before), drink 150-250mL every 15-20 minutes during exercise, rehydrate after. Rehydration: for every kg of body weight lost during exercise (weigh before and after), drink 1.5 litres to fully replace (including ongoing losses). Electrolyte
Signs of Dehydration
Mild dehydration (1-2% body weight): thirst, slightly concentrated urine (yellow), reduced concentration. These symptoms often appear after dehydration has already begun — thirst is a lagging indicator. Moderate dehydration (3-5%): headache, reduced physical and cognitive performance, darker urine. By the time you feel thirsty during exercise, performance may already be impaired. Severe dehydration (>5%): confusion, rapid heart rate, dizziness — medical emergency. Urine colour: the best simple h
Can You Drink Too Much Water?
Hyponatraemia (water intoxication): drinking excessive water can dilute blood sodium to dangerous levels. Most common in: endurance athletes drinking large amounts of plain water over several hours. Symptoms: headache, nausea, confusion, seizures. Prevention: use electrolyte drinks for events over 90 minutes. Drink to thirst, not to a rigid schedule during long events. Risk for most people: very low — kidneys can process approximately 800-1,000mL per hour. Drinking 2-3 litres spread throughout t
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