Background: Drinking water is often applied as a dietary means for weight loss and overweight/obesity prevention, but no evidence-based recommendation exists for this indication.

Objective: We summarized the existing evidence on the association between water consumption and body weight outcomes in adults of any body weight status.

Design: In a systematic review, we retrieved studies from 4 electronic databases (MEDLINE, EMBASE, CINAHL, and COCHRANE), cross-references by PubMed functions and hand-searching, and experts' recommendations. Any type of study including adults aged >18 y that reported the association between daily water consumption and any weight-related outcome, such as body weight, body mass index, or body weight classifications, was eligible.

Results: Of 4963 retrieved records, 11 original studies and 2 systematic reviews were included. In participants dieting for weight loss or maintenance, a randomized controlled trial, a nonrandomized controlled trial, and an observational longitudinal study showed that increased water consumption, in addition to a program for weight loss or maintenance, reduced body weight after 3-12 mo compared with such a program alone. In mixed-weight populations not primarily dieting for weight loss or maintenance, 2 short-term randomized trials showed no effect of water consumption on body weight; 6 cross-sectional studies showed inconsistent results.

Conclusions: Studies of individuals dieting for weight loss or maintenance suggest a weight-reducing effect of increased water consumption, whereas studies in general mixed-weight populations yielded inconsistent results. The evidence for this association is still low, mostly because of the lack of good-quality studies. This trial was registered at www.crd.york.ac.uk/Prospero as CRD42012002585.