Hydration: How Much Water Do You Need?

Advice about water is everywhere: eight glasses a day, a gallon a day, drink before you're thirsty, drink to "flush out" fat. Some of it is helpful, and some of it is overstated.

This guide covers how much fluid most men need, what counts, how to tell if you're drinking enough, and what water can realistically do for fat loss and training.

How much water do men need?

Official guidance gives a useful starting point:

• The European Food Safety Authority (EFSA) suggests about 2.5 litres of total water a day for adult men. That includes water from food, which usually provides around 20% of the total.
• The NHS suggests 6 to 8 cups or glasses of fluid a day for most people.
• US guidance from the National Academies suggests about 3.7 litres a day of total water for men, again including food.

In practice, that works out at roughly 2 to 2.5 litres of fluid from drinks a day for most healthy men in a temperate climate, with more needed in some situations. These are general estimates, not targets you need to hit exactly.

You need more when

• It's hot or humid
• You're exercising and sweating, especially for longer than an hour
• You're at high altitude
• You're ill with a fever, vomiting or diarrhoea
• You're a larger or very active person

What counts

Almost all drinks count towards your fluid intake:

• Water, still or sparkling
• Tea and coffee. Moderate amounts don't dehydrate you, despite the common myth. Keep total caffeine sensible (caffeine and training covers safe amounts) and avoid it late in the day. Sleep and fat loss explains why that matters.
• Milk, which also provides protein
• Sugar-free drinks

Food also provides water, particularly fruit, vegetables, soups, yoghurt and stews.

Alcohol is the exception. It increases urine output, so it's not a good way to hydrate. Alcohol and fat loss explains its other effects.

Simple ways to check

You don't need to measure every glass. For most healthy people, two simple checks work well:

1. Urine colour. Pale straw or light yellow usually means you're well hydrated. Dark yellow or amber suggests you need more. (Some vitamins and foods can change urine colour.)
2. Thirst. For most healthy adults, drinking when you're thirsty and with meals is enough.

Signs you may be short on fluid include thirst, dark urine, headaches, tiredness and dizziness.

Water and fat loss

Water doesn't burn fat, and it doesn't "flush" fat out of your body. But it can help in a few practical ways:

• Replacing sugary drinks. Swapping one regular fizzy drink, juice or sweet coffee a day for water or a zero-calorie drink is one of the simplest fat-loss changes there is. Liquid calories don't fill you up the way food does.
• Fullness before meals. Some research has found that drinking a glass or two of water before meals slightly reduces how much people eat. The effect is modest, but it's an easy habit.
• Training quality. Even mild dehydration can make workouts feel harder. Staying hydrated helps you train well, which supports keeping muscle while you lose fat.

Water and the scale

Your body weight can swing by a kilogram or more from day to day because of changes in water, salt and stored carbohydrate. Drinking more or less water on a given day can affect the scale, but it doesn't change your body fat. Water weight vs fat loss explains these fluctuations, and why weekly averages are more reliable than daily weigh-ins.

Hydration for training

For most workouts under an hour, water is all you need:

• Drink normally through the day so you start your session well hydrated.
• Sip water during your workout, especially if you're sweating heavily.
• Drink afterwards to replace what you've lost.

For long or very sweaty sessions, particularly in the heat, drinks or foods that include some salt (sodium) can help replace what you lose in sweat. Most people training for under an hour don't need sports drinks, which also contain sugar and calories.

Easy habits

• Keep a water bottle at your desk, in your bag or in the car.
• Drink a glass of water with every meal.
• Start the day with a glass of water alongside your coffee or tea.
• Choose water or sugar-free drinks by default, and save juice and fizzy drinks for occasional treats.

Can you drink too much?

Yes, although it's uncommon in everyday life. Drinking very large amounts of water in a short time can dilute the sodium in your blood, a condition called hyponatraemia, which can be serious. It's most often seen in endurance events when people drink far more than they sweat out. There's no need to force down large volumes. Drink to thirst, and a bit more when it's hot or you're training.

The bottom line

Most healthy men need roughly 2 to 2.5 litres of fluid a day from drinks, more in the heat or when training hard. Water, tea, coffee and milk all count. Check your urine colour, drink with meals and when you're thirsty, and swap sugary drinks for water. It won't burn fat, but it makes a deficit easier and helps you train well. Nutrition fundamentals for fat loss shows how it fits with everything else.