Water is not a weight-loss formula.
Some trials suggest benefits in specific settings. They do not establish a personal water target for losing weight.
What the review found
A 2024 review by Chen QY, Khil J and Keum N included eight randomized trials in people with overweight or obesity. The pooled weight difference was −0.33 kg, with a 95% confidence interval from −1.75 to +1.08 kg. That interval includes no effect.
The studies used different interventions, including adding water and replacing other drinks. Results varied substantially. The pooled number should not be presented as a promised loss of a third of a kilogram.
Why you may have heard a different number
A 2010 trial by Dennis and colleagues reported greater weight loss with premeal water alongside a reduced-calorie diet in middle-aged and older adults. That result describes a particular intervention and population; it does not establish a universal effect of drinking more water.
How newer reviews fit together
Hakam and colleagues, JAMA Network Open (2024), reviewed 18 trials across several health outcomes. Some adult weight-loss trials reported benefits, but populations and interventions differed, so the authors did not pool the studies into a meta-analysis. Their search ended in April 2023. These findings do not establish an optimal total daily intake.
Davy and colleagues, Physiology & Behavior (2025), discuss recent reviews and possible mechanisms such as appetite effects and beverage substitution. This is a narrative overview, not a new trial or meta-analysis. It includes work from the authors’ own team and describes ongoing research; those planned results are not evidence of benefit yet. The best volume and timing remain uncertain.
Replacing sugary drinks is a different decision
The review suggests that replacing sugar-sweetened beverages with water may offer a modest benefit. This is different from adding extra water to an otherwise unchanged diet.
No special calculator for losing weight
We do not prescribe extra water for fat loss or ask you to recalculate a target after each weight change. Our daily converter shows a general adult reference, with the same limitations whether or not you are trying to lose weight.
Evidence reviewed September 7, 2026. See our method and limits.