The situation here is not identical, but it is very close. The proposition before us is that the Torah prohibits drinking a glass of perfectly clear water in which no one has ever observed a forbidden substance. Even if, as some have reported, a trained observer can sometimes see a copepod in a glass of water, it is hard to imagine that such a phenomenon, which virtually no one noticed for generations, constitutes a reasonably common minority of cases (a mi’ut ha’matzuy).
Moreover, copepods are present in many lakes throughout the world and surely have been for centuries. It may well be that the percentage of these creatures in New York City tap water is higher than the percentage in a bucket of water drawn from the upper level of a lake. While such a distinction can have halachic consequences, it does not change the fact that innumerable glasses of water containing copepods have been consumed by pious and learned Jews through the ages.
The paucity of halachic literature on this issue underscores the obvious: in almost all cases, these Jews drank the water in question without noticing anything amiss.
To return, then, to New York City, we are being told that the Torah forbids what Rav Aharon Kotler, Rav Moshe Feinstein, Rav Yosef Dov Soloveitchik, Rav Avraham Pam, Rav Yaakov Kaminetsky, and a galaxy of chassidic rebbes from Satmar to Bobov to Lubavitch to Skver, drank without the slightest hesitation as a result of their failure to investigate the content of this perfectly clear glass of water.
Shall we describe them as anusim, i.e., people with no meaningful recourse to information about these entities, which are nonetheless biblically forbidden? Or shall we describe them as shogegim, i.e., inadvertent sinners who should have been more diligent in investigating the content of the water that they regularly drank? It is difficult to contemplate either of these alternatives without a sense of the most profound unease.