Water Intake Calculator UK | Daily Hydration Calculator 2025
Free UK Water Intake Calculator. Calculate exactly how much water you should drink daily based on your weight, activity level, and climate.
Last updated: February 2026
Water Intake Calculator UK 2025
Calculate your recommended daily water intake based on your body weight, activity level, and climate. Our calculator follows NHS hydration guidelines and provides personalised recommendations for optimal health.
Enter your weight in kilograms
Older adults may need extra reminders to hydrate
Quick Reference: Daily Water Needs by Weight
| Body Weight | Sedentary | Moderate | Active |
|---|---|---|---|
| 50 kg (7st 12lb) | 1.75 litres | 2.1 litres | 2.5 litres |
| 60 kg (9st 6lb) | 2.1 litres | 2.5 litres | 3.0 litres |
| 70 kg (11st) | 2.45 litres | 2.9 litres | 3.5 litres |
| 80 kg (12st 8lb) | 2.8 litres | 3.4 litres | 4.0 litres |
| 90 kg (14st 2lb) | 3.15 litres | 3.8 litres | 4.5 litres |
NHS Hydration Guidelines
The NHS recommends drinking 6-8 glasses (approximately 1.2-2 litres) of fluid per day. This includes water, lower-fat milk, and sugar-free drinks like tea and coffee. In hot weather or during exercise, you'll need more. Foods like fruits, vegetables, and soups also contribute to your daily fluid intake.
Why Proper Hydration Matters
Water is essential for virtually every function in your body. Staying properly hydrated supports:
- Brain function: Even mild dehydration (1-2%) can impair concentration, mood, and memory
- Physical performance: Losing just 2% of body water can reduce exercise capacity by up to 25%
- Digestion: Water helps break down food and prevents constipation
- Kidney health: Adequate hydration helps flush toxins and reduces kidney stone risk
- Skin health: Proper hydration keeps skin looking healthy and may reduce wrinkle appearance
- Temperature regulation: Sweating requires adequate water to cool the body effectively
- Joint lubrication: Cartilage is about 80% water, keeping joints moving smoothly
Pro Tip: Check Your Urine
The easiest way to check your hydration status is by observing your urine colour. Pale straw or light yellow indicates good hydration. Dark yellow or amber suggests you need to drink more. First thing in the morning, urine is naturally more concentrated, so check later in the day for a better indication.
Signs of Dehydration
Recognising dehydration early helps prevent more serious health issues. Watch for these warning signs:
Dark Urine
Dark yellow or amber coloured urine
Headaches
Frequent headaches, especially in afternoon
Fatigue
Feeling tired despite adequate sleep
Dry Mouth
Dry mouth, lips, and skin
Poor Focus
Difficulty concentrating
Dizziness
Feeling lightheaded when standing
When to Seek Medical Help
Severe dehydration requires medical attention. Symptoms include: not passing urine for 8+ hours, rapid heartbeat, confusion, sunken eyes, or fainting. Elderly people and young children are particularly vulnerable to dehydration.
Sample Daily Hydration Schedule
Spreading your water intake throughout the day is more effective than drinking large amounts at once. Here's a sample schedule for someone needing 2.5 litres daily:
Hydration Tips for Office Workers
Keep a water bottle at your desk as a visual reminder. Set hourly reminders on your phone. Drink a glass of water before each meal. Replace one caffeinated drink with water each day. Walk to the water cooler for regular movement breaks.
What Counts Towards Your Fluid Intake?
Best Choices
- Water: The best choice - no calories, sugar, or additives
- Herbal teas: Caffeine-free and count fully towards intake
- Lower-fat milk: Provides hydration plus calcium and protein
- Sugar-free squash: Good alternative if you struggle with plain water
Moderate Choices
- Tea and coffee: Count towards intake, but watch caffeine levels (NHS says they count!)
- Fruit juice: Limit to 150ml daily due to sugar content
- Sparkling water: Fine as alternative to still water
Limit These
- Sugary drinks: High in empty calories
- Energy drinks: Often high in caffeine and sugar
- Alcohol: Has diuretic effect, so drink extra water to compensate
Food Contributes Too!
About 20% of our daily fluid intake comes from food. Water-rich foods include: cucumber (96% water), lettuce (95%), celery (95%), tomatoes (94%), watermelon (92%), strawberries (91%), and oranges (87%). Soups and stews also contribute significantly.
When You Need Extra Water
During Exercise
- Drink 400-600ml 2-3 hours before exercise
- Drink 200-300ml every 15-20 minutes during activity
- For activities over 1 hour, consider electrolyte drinks
- Weigh yourself before and after - drink 500ml for every 0.5kg lost
Hot Weather
- Increase intake by 20-30% on hot days
- Don't wait until you're thirsty to drink
- Carry a water bottle when outdoors
- Be extra vigilant in air-conditioned environments (can be dehydrating)
Illness
- Fever, diarrhoea, and vomiting all increase fluid needs
- Consider oral rehydration solutions for severe cases
- Small, frequent sips are often better tolerated than large amounts
Pregnancy & Breastfeeding
- Pregnant women need about 300ml extra daily
- Breastfeeding mothers need approximately 700ml extra daily
- Signs of dehydration can affect milk production
Frequently Asked Questions
The NHS recommends drinking 6-8 glasses (1.2-2 litres) of fluid per day in typical UK conditions. However, individual needs vary based on body weight, activity level, and climate. A more accurate calculation is 35ml per kilogram of body weight as a baseline. So a 70kg person would need about 2.45 litres as a starting point, adjusted for activity and conditions.
Yes, according to the NHS, tea and coffee do count towards your daily fluid intake. While caffeine has mild diuretic effects, studies show the fluid content of these drinks still contributes to overall hydration. However, water remains the healthiest choice as it contains no calories, sugars, or additives. If you drink large amounts of caffeinated drinks, consider having extra water to balance out.
Yes, drinking too much water too quickly can cause hyponatremia (water intoxication), where blood sodium levels become dangerously low. However, this is rare and typically only occurs when drinking several litres in a short period (like during extreme endurance events). For most people, spreading intake throughout the day and drinking when thirsty is perfectly safe. Listen to your body's signals.
Both are fine for hydration. Some people find cold water more refreshing and may drink more of it. Cold water may slightly boost metabolism as your body works to warm it. Room temperature water is often easier to drink quickly during exercise. There's no significant difference for health - drink whatever temperature you prefer and will consume more of.
Yes, absolutely. Aim to drink 400-600ml of water 2-3 hours before exercise, 200-300ml every 15-20 minutes during activity, and continue hydrating after exercise. For activities lasting over an hour, consider drinks with electrolytes to replace salts lost through sweat. A good rule of thumb is to drink 500ml for every 0.5kg of body weight lost during exercise.
The easiest indicator is urine colour. Pale straw or light yellow indicates good hydration. Dark yellow or amber means you need more fluids. Other signs of adequate hydration include: rarely feeling thirsty, having moist lips and mouth, good energy levels, and regular bathroom visits (approximately 4-7 times per day for most adults).
Last updated: February 2026 | Reviewed annually for accuracy
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- 2025/26 updated - Using current rates and regulations
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