Daily Water Intake & Hydration Calculator
Calculate your personalised daily water intake based on body weight, activity level, climate, and health status.
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Hydration Guide
What should I know about 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 drinks specifically, with the remainder naturally covered by a typical varied diet.
What do I need to know about 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 drinks become more important the longer and harder the session, since plain water alone can't replace the sodium and other minerals lost through heavy sweating.
What should I know about 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 home check — pale straw colour generally indicates good hydration, while dark yellow or amber suggests you need to drink more.
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 the day poses essentially no risk for a healthy adult — the real danger comes from drinking very large volumes in a very short time, which is rare outside extreme endurance events.