Does drinking more water help you lose weight?

Short answer

Water itself does not burn fat. But 500 ml of water before meals makes you eat less at that meal, and alongside a diet plan it led to 1.3-2 kg more weight loss over 12 weeks.

Does drinking more water help you lose weight?
'Water → faster metabolism → less fat' — does this formula hold?
A common claim is that drinking lots of water speeds up your metabolism and melts fat. We checked, step by step, whether water really burns calories and whether people actually lost more weight.
The study that said water raises metabolism 30%
About 24 kcal per 500 ml
When 14 people drank 500 ml of water, their metabolic rate rose 30%, adding about 100 kJ (about 24 kcal). About 40% of that went into warming 22-degree water to body temperature. This study became the go-to evidence for 'water diets.'
Measured again, metabolism did not rise
No change with room-temperature water; 4.5% with 3-degree water
In another study, room-temperature water did not raise metabolism, and only water chilled to 3 degrees raised it, by 4.5% over 60 minutes. In a study of 27 people drinking 500 ml, there was no difference from just pretending to drink. Water itself did not burn fat.
But drinking before meals led to more weight loss
A 1.3-2 kg difference over 12 weeks
48 people on a low-calorie diet drank 500 ml of water before every meal and lost about 2 kg more over 12 weeks than those who didn't. In another study, 84 people drinking 500 ml 30 minutes before meals also lost 1.3 kg more over 12 weeks.
The reason was eating less
After 500 ml of water, a meal dropped from 541 kcal to 498 kcal
When the same 48 people ate freely, a meal after 500 ml of water dropped from 541 kcal to 498 kcal. Water did not raise metabolism; it filled the stomach and cut intake. After 12 weeks the gap had shrunk (506 kcal vs 480 kcal).
Just telling people to drink more made little difference
Pooling 8 studies: 0.33 kg
Pooling 8 studies that had people drink more water, or drink water instead of other drinks, the weight difference was 0.33 kg, which was not meaningful. The biggest difference among them came from swapping sugary drinks for water (0.81 kg).
Bottom line: water doesn't burn fat, it helps you eat less
500 ml before meals, 1.3-2 kg over 12 weeks
Water itself barely raised metabolism. But alongside a diet plan, 500 ml before meals cut how much people ate and led to 1.3-2 kg more loss over 12 weeks. Simply drinking more made a difference of only 0.33 kg.