https://skepticalinquirer.org/2011/05/the-memory-of-water/
https://rationalwiki.org/wiki/Water_memory
Water memory is one of the concepts central to modern (i.e., post-Avogadro)
homeopathy.
Due to the nature of the dilutions in a homeopathic preparation, no
molecule of any active ingredient remains in the final product.
[note 1] To get around this fact, homeopaths fall back onto the idea that the solution somehow retains a "memory" of the solute (rarely is an explanation given for why the mere
memory of a substance should be better at performing a given task than the
actual substance itself). Although it is possible to argue that only proof of efficacy in homeopathic preparations is important, water memory has become an essential element for anyone trying to offer up
rationalizations for a mechanism of action. To highlight its importance, the homeopathic apologist's journal
Homeopathy devoted a whole issue to water memory.
[1]
This idea takes many forms,
each of which is less plausible than the last.
Summary
The completely unscientific nature of these hypotheses has been explored elsewhere, but they have a number of flaws in common. The explorations start with the assumption that the phenomenon in question actually exists, and moves from there to try to find a reason why it exists. None of these reasons have any scientific plausibility. Furthermore, the experiments fail to provide adequate
control and rigorous determinations of purity, and fail to assess error in the measurements. The proponents also give possible explanations of the phenomenon without any link between their "data" and the proposed physical explanations. Explanations include increased or decreased levels of hydrogen bonding; macroscopic clustering of water molecules; and polymerization (which is impossible unless you have the right trading card in your hand).
