There is a new device that has been installed in mikvehs in order to clean them and destroy the bacteria in them. The device mixes oxygen from the air into the water, thereby changing the structure of the water, such that during the process the water is transformed into hydroxyl and then returns again to the state of ordinary water, and in the course of the process the water is cleaned and disinfected. A small group of rabbis has arisen claiming that this disqualifies the water from being considered water under the Jewish-law distinction between water and other liquids explained in halakhah. One of the central arguments for permitting it is based on the fact that the human eye does not detect any change in the water. Accordingly, it is argued that in light of all the proofs and arguments that it is the human eye, and not the scientific definition, that measures phenomena from a halakhic standpoint, the water is ordinary water—as determined by the human eye. In that connection, the Hazon Ish’s argument about the two thousand years of Torah was mentioned as one of many considerations for why the human eye is determinative. In my question I qualified things and said that I was speaking according to the view that phenomena are indeed generally measured by the human eye. That is because I assumed that this very determination is presumably not absolute or universally agreed upon. Now those who forbid it are claiming to exclude the present case from that categorical rule: they say that the rule is valid only for natural phenomena or things made by man that could have been created in accordance with the knowledge available during the two thousand years of Torah; but with a phenomenon produced by a machine invented in our time, which creates a new phenomenon, one cannot claim that it should again be examined by the human eye. Rather, what is produced by a new scientific instrument should be measured by the tools of science. Is that argument valid?

The argument is valid, meaning its conclusion follows from its premises. But I don’t agree. First, the Hazon Ish’s words seem unfounded to me in themselves. But even aside from the Hazon Ish, if to the eye it looks like water, then it is water. We even find in Mishnah Mikvaot: “If their appearance was like the appearance of water…” Appearance is what determines it.

So then someone who immerses in liquid nitrogen has fulfilled his obligation.