Water will not burn fat. But a few simple habits around drinking make a deficit easier to keep. You do not have to force down extra litres. You just need to do a few things properly.
Short answer: Roughly 30 to 35 ml per kilogram of body weight a day. For a person who weighs 80 kg, that comes to about 2.4 to 2.8 litres. If you train or it is hot outside, add more. If your doctor has told you to limit fluids (for example with heart or kidney problems), follow their advice, not this guide. The same goes for pregnancy and breastfeeding: ask your doctor how much you should drink. The easiest check is the colour of your urine: light yellow is fine, dark yellow usually means you need to drink more.
Why water matters
Water is involved in everything in the body, from digestion to how you perform in the gym. When you are short on it, you get tired, you focus worse, and you may not perform as well in training.
Then there is one thing the brain can mix up: sometimes thirst can feel a bit like hunger. So before you reach for a snack, have a glass of water and wait a moment. Check whether it was just thirst. More on telling real hunger apart is in cravings and hunger.
How much to drink
Spread it across the day rather than drinking a lot at once: a glass in the morning, one with each meal, and some around training. On a training day or a hot day, add more.
You do not need to measure every glass. Light yellow urine is fine. Dark yellow usually means you need to drink more. Some vitamins, medications and foods change the colour too. If your urine stays dark or turns brown even when you drink enough, see a doctor.
Liquid calories: easy to miss
Liquid calories are one of the easiest places to lose your deficit without noticing. Sweet soft drinks, juice, sweetened coffee or alcohol put hundreds of kcal (calories) into you, and they fill you up much less than food. One glass of soda plus a small beer is roughly 250 kcal. That can be about half of a typical day's deficit, without you eating a thing.
If you want the numbers on drinks in particular, see alcohol and fat loss and diet soda and weight loss.
Does water really help you lose fat?
Do not expect miracles. But it can help, indirectly.
- Drinking water before a meal (around two glasses) can fill you up a little, so you may eat a bit less. The effect is small and varies from person to person.
- Swap sweet drinks for water and you save calories, without giving up anything on your plate.
How big your deficit should be in the first place is in calorie deficit: how much to eat, or you can work it out with the calculator.
Practical tips
- Keep a bottle where you can see it. What you see, you drink.
- One or two glasses of water before meals.
- Swap sweet drinks for water or unsweetened tea.
- Coffee and tea count toward your daily fluids. Alcohol does not really help here, and it adds calories, so keep it low.
Drinking water on its own will not make anyone lose fat. But it makes the whole process a lot easier. It is one of the simplest habits you can start today.
Frequently asked questions
Does drinking water help you lose weight?
Do not expect miracles, but it can help indirectly. Drinking water before a meal (around two glasses) can fill you up a little, so you may eat a bit less. And when you swap sweet drinks for water, you save calories.
Why are liquid calories a problem when losing fat?
Sweet soft drinks, juice, sweetened coffee or alcohol give you hundreds of calories that fill you up much less than food. A glass of soda plus a small beer can eat up around half of a typical daily deficit, without you eating anything.
Can I mistake thirst for hunger?
It can happen. Before you reach for a snack, have a glass of water and wait a moment to see if it was just thirst.
What happens if I drink too little?
When you are short on water, you get tired, you focus worse, and your training suffers.
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1) Guideline used in the article: about 30 to 35 ml of water per kilogram of body weight per day, more with exercise or heat; urine colour as a simple check
Martin Barna
Online nutrition and fitness coach. Since 2013 I have coached 600+ people. Evidence-based nutrition and training.
Apply for coachingThis article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.