Water memory is the claimed ability of water to retain a "memory" of substances previously dissolved in it to arbitrary dilution. No scientific evidence supports this claim.Shaking the water at each stage of a serial dilution is claimed to be necessary for an effect to occur. The concept was proposed by Jacques Benveniste to explain the purported therapeutic powers of homeopathic remedies, which are prepared by diluting solutions to such a high degree that not even a single molecule of the original substance remains in most final preparations. Benveniste sought to prove this basic tenet of homeopathy by conducting an experiment to be published "independently of homeopathic interests" in a major journal.

While some studies, including Benveniste's, have reported such an effect, double-blind replications of the experiments involved have failed to reproduce the result. The concept is not consistent with accepted scientific laws and is not accepted by the scientific community. Liquid water does not maintain ordered networks of molecules for longer times than a small fraction of a nanosecond.