Water Intake Calculator
Find out how much water your body needs each day. Based on your weight, activity level, climate, and health status — not just the generic "8 glasses a day" rule.
Special conditions (add extra needs)
Your daily water target
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litres per day
— ml · — cups (240 ml)
Base need
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ml
Activity add
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ml
Climate / other
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ml
Hourly sip reminder (over 16 waking hours)
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ml per hour
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glasses (240 ml) per day
Based on the EFSA AI of 35 ml/kg body weight, adjusted for activity and conditions. Food provides ~20% of daily water — this figure covers beverages only. Not medical advice.
How much water do you really need?
The oft-cited "8 glasses a day" (about 2 litres) is a rough average — not a personalised recommendation. The European Food Safety Authority (EFSA) and the Institute of Medicine (IOM) both set Adequate Intakes (AI) based on body weight: approximately 35 ml per kg of body weight per day for adults, adjusting upward for higher activity, heat, and certain health conditions.
This figure includes water from beverages only. Food typically contributes another 20% of daily water intake (fruit, vegetables, soups), so total water needs are slightly higher than beverage intake alone.
Signs of dehydration
Mild dehydration (as little as 1–2% body mass loss) can impair concentration, mood, and physical performance. Key signs include dark yellow urine, dry mouth, fatigue, and reduced urine frequency. The simplest indicator: aim for pale straw-coloured urine throughout the day.
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