The NHS recommends drinking 6–8 glasses of fluid per day — approximately 1.5 to 2 litres for most adults. But that number is a population-wide average, not a personal prescription. A 60kg person who works at a desk has very different needs to a 90kg runner.
This guide explains where the 6–8 glasses figure comes from, how to calculate a more accurate daily target for your body, and what actually counts toward it.
💧The NHS Guideline: 6–8 Glasses Per Day
The NHS fluid recommendation is deliberately broad. Six to eight cups or glasses per day covers the baseline needs of a typical sedentary adult in a temperate climate. That works out to roughly:
- 1.5 litres at the low end (six 250ml glasses)
- 2 litres at the high end (eight 250ml glasses)
All fluids count toward this target — water, tea, coffee, milk, juice, and even soup. The NHS does not insist on plain water only, though it is the healthiest choice for dental health and avoiding excess calories.
This figure has been consistent across NHS guidance for years and broadly aligns with European Food Safety Authority (EFSA) recommendations of 2L per day for women and 2.5L for men.
How to Calculate Your Personal Daily Water Intake
The 6–8 glasses rule ignores body weight and activity. A more personalised formula used by sports scientists and dietitians:
Daily water intake (ml) = Body weight (kg) × 35ml
Add 500–750ml for every hour of moderate exercise
Examples:
| Body weight | Sedentary target | + 1hr exercise |
|---|---|---|
| 60 kg | 2,100 ml (2.1L) | 2,600–2,850 ml |
| 75 kg | 2,625 ml (2.6L) | 3,125–3,375 ml |
| 90 kg | 3,150 ml (3.15L) | 3,650–3,900 ml |
So a 90kg person has a daily water requirement around 57% higher than a 60kg person — yet both fall within the NHS's "6–8 glasses" guidance because it is so broad.
Use the calculator below to get your number instantly:
💧Factors That Increase Your Daily Water Needs
The 35ml-per-kg baseline assumes a temperate climate and moderate activity. Adjust upward for:
Exercise Sweat losses during exercise range from 0.5 to 2 litres per hour depending on intensity and temperature. A practical rule: add 500ml for every 30 minutes of moderate exercise (running, cycling, gym). Drink during exercise, not just after.
Hot weather In summer or in a heated office, you can lose an extra 0.5–1 litre per day through sweating without noticing. When the temperature climbs above 25°C, add at least 500ml to your baseline.
Illness Fever, vomiting, and diarrhoea cause rapid fluid loss. A single day of moderate gastroenteritis can deplete you by 1–2 litres on top of normal losses. The NHS recommends frequent small sips of water or oral rehydration salts when unwell.
Pregnancy and breastfeeding Pregnant women are advised to drink around 300ml more than usual per day. Breastfeeding increases needs significantly — producing milk requires around 700ml of extra fluid daily.
High-altitude environments Breathing is faster at altitude, which increases water loss through respiration. Add 500–1,000ml per day when above 2,500 metres.
Signs You Are Not Drinking Enough
Thirst is a late signal — by the time you feel thirsty, you are already mildly dehydrated. The most reliable indicators:
Urine colour is the easiest marker. The NHS recommends checking it regularly:
| Colour | Hydration status |
|---|---|
| Pale straw yellow | Well hydrated |
| Yellow | Adequate |
| Dark yellow/amber | Drink more |
| Brown or orange | Severely dehydrated — drink water immediately |
Other signs of dehydration:
- Headache (one of the earliest symptoms)
- Reduced concentration and fatigue
- Dry mouth and lips
- Dizziness on standing
- Reduced urine output or no urination for 8+ hours
Mild dehydration — as little as 1–2% of body weight lost as fluid — measurably impairs cognitive performance and mood in studies. It does not feel dramatic, which is why it often goes unnoticed.
Does Coffee and Tea Count?
Yes — despite their mild diuretic effect, caffeinated drinks do contribute to your overall fluid intake. Several large studies, including one from the University of Birmingham, found that moderate coffee consumption (3–4 cups/day) produces the same net hydration as water.
The NHS includes tea and coffee in its recommended 6–8 cups per day. That said:
- Do not replace water entirely with caffeinated drinks. Caffeine has a threshold above which net fluid loss increases — around 400mg (approximately 4 espressos) per day.
- Sugary drinks count but come with a cost. A 330ml can of cola contributes ~330ml of fluid but also ~35g of sugar.
- Alcohol does not count. Alcohol suppresses the hormone that controls urine production (ADH), causing net fluid loss — this is why drinking alcohol is dehydrating.
Can You Drink Too Much Water?
Yes, though it is rare in healthy adults who are not competing in endurance events.
Drinking excessive water in a short period can dilute sodium levels in the blood, causing hyponatraemia — low blood sodium. Symptoms include nausea, headache, confusion, and in severe cases, seizures or death. This typically only occurs when consuming 3–4 litres within a few hours, or in endurance athletes who drink too much plain water during events longer than 4 hours.
For most people following the 35ml-per-kg guideline and drinking to thirst, this is not a concern.
People who should follow medical advice on fluid intake: Chronic kidney disease, heart failure, and certain liver conditions all require specific fluid restrictions. If you have been diagnosed with any of these, follow your GP or dietitian's guidance rather than general population recommendations.
Hydrating Foods: What Counts Beyond Drinks
Roughly 20–30% of daily water intake in UK adults comes from food. Fruits and vegetables are particularly high in water content:
| Food | Water content |
|---|---|
| Cucumber, lettuce, celery | 95–97% |
| Watermelon, strawberries | 91–92% |
| Oranges, grapefruit | 86–88% |
| Cooked oatmeal, soup | 84–90% |
| Chicken breast (cooked) | ~65% |
A diet rich in fruits and vegetables naturally contributes several hundred millilitres toward your daily total. This is not a reason to drink less water — but it does explain why people in Mediterranean countries, who eat more fresh produce, can sustain good hydration on seemingly modest water intake.
Practical Tips for Hitting Your Daily Target
Most people who say they "can't drink enough water" have a habit problem, not a preference problem. Three things that actually work:
1. Drink a glass first thing in the morning. You lose around 0.5 litres overnight through breathing and sweating. Starting the day with 400–500ml immediately puts you ahead.
2. Tie drinking to meals. A glass before each of three meals is 750ml. Add a glass mid-morning and mid-afternoon and you are at 1.25 litres — the rest comes from food and other drinks.
3. Track urine colour, not volume. Rather than counting glasses, check your urine in the morning and afternoon. If it is consistently pale yellow, you are on track. Dark yellow means drink more.
Hydration and Your Overall Health
Staying well hydrated works best alongside a complete picture of your health. If you want to check whether your weight is in a healthy range for your height, our BMI Calculator gives you your NHS category and healthy weight range instantly. For a full explanation of what your number means — including ethnicity-adjusted thresholds and waist circumference guidance — read: What is a Healthy BMI? UK NHS Weight Ranges Explained.
Frequently Asked Questions
Is 2 litres of water a day enough? For most adults at rest in a temperate climate, 2 litres meets the NHS guideline. Whether it is enough specifically for you depends on your weight and activity level. A 90kg person who exercises daily needs closer to 3–4 litres. Use the water intake calculator above to get a personalised figure.
Should I drink more water to lose weight? Drinking water before meals has been shown in some studies to reduce calorie intake by creating a temporary sense of fullness. It also has no calories. However, water does not directly increase fat loss — that is driven by calorie deficit. Staying hydrated does support exercise performance, which indirectly supports weight management.
Is it better to sip water throughout the day or drink large amounts? Sipping regularly is generally better for hydration than drinking large amounts in one sitting. The kidneys can only process around 0.8–1 litre per hour — excess beyond this is excreted. Spreading intake across the day keeps your cells consistently hydrated.
Can you get enough water from food alone? Not typically for UK adults. While 20–30% of daily intake comes from food, you would need to eat very large quantities of high-water produce to fully replace drinks. In practice, food hydration supplements drinks — it does not replace them.
Does water intake change with age? Older adults have a diminished sense of thirst and are at higher risk of dehydration, even without feeling thirsty. The NHS specifically recommends that people over 65 make a conscious effort to drink regularly throughout the day, not just when thirsty. Dementia and certain medications can further reduce the thirst response.