Question: You have explained in a previous Halacha that Chametz on Pesach can never be nullified by any ratio. If so, how is it permissible to drink water from lakes, such as the Kinneret, in which there are certainly crumbs of Chametz?
Answer: We have explained that Chametz on Pesach is not nullified even by a ratio of one to one-thousand. This means that if even a tiny crumb of Chametz falls into a large pot filled with food on Pesach, the entire pot of food becomes forbidden. This is something that we never find by any other prohibition, for when a small amount of prohibited food falls into a larger amount of permissible food, it is usually nullified by a ratio of one to sixty. For instance, if a drop of milk accidentally spills into a large pot of meat soup, the soup is permissible for consumption since there is certainly at least sixty times more than the drop of milk in the soup. Our Sages ruled stringently with regards to Chametz that it cannot be nullified at all since the Torah was also extremely stringent about the prohibition of Chametz on Pesach, for one who consumes Chametz incurs the “Karet” punishment in addition to the fact that the Torah prohibited even ownership of Chametz on Pesach.
Thus, most places have an issue for most centralized water sources contain some Chametz particles in them. Based on this, it should be forbidden to drink such water on Pesach, for this should be considered a Chametz mixture. There are indeed pious individuals who act stringently in this regard and fill up large tanks with enough water to last them the entire Pesach before Pesach begins and they do not use water from the tap on Pesach for the above reason.
Indeed, over forty years ago, people began raising awareness that there were several restaurants along the banks of the Kinneret (Sea of the Galilee) in northern Israel which would throw bread into the lake on Pesach itself. When Maran zt”l served as Chief Rabbi of Israel, he went and inspected this on his own. When he realized that the claims were actually correct, he penned a response on this topic.
This issue was first discussed approximately two-hundred years ago by Hagaon Harav Yehoshua Heschel of Tarnipol, author of the Sefer Yehoshua, and he writes that in Jewish communities along rivers, non-Jews throw bread into the river all throughout Pesach and this creates a problem of Chametz mixtures. He writes that this was the case in the city of Dubno along whose river ran a water-powered mill and the non-Jews would dump the chaff and bran into the river. Similarly, the leftover beer they produced there from barley would be spilled into the river as well. If so, the river should thereby constitute a Chametz mixture.
The great author of the Sefer Yehoshua inquired about this from Hagaon Harav Yaakov Loberbaum of Lisa, author of the Chavot Da’at, and the later ruled leniently on the matter since the water was constantly flowing at a fast pace and the Chametz did not have the opportunity be steeped in it; thus, this cannot be considered a Chametz mixture. Hagaon Harav Yehoshua Heschel himself added a different reason for leniency which was that the only reason why the Sages ruled that Chametz is not even nullified by a ratio of one to one-thousand is because they were concerned about a situation where the Chametz might actually add flavor to the mixture. However, with regards to a tremendous river where it is impossible for Chametz to add any flavor to the water, they did not enact that the Chametz should not be nullified.
Nevertheless, because these rationales were novel, the author of the Sefer Yehoshua writes that he is hesitant to rely on these leniencies with regards to Chametz on Pesach. On the other hand, the author of the Yad Yehuda writes that the ruling of the Sefer Yehoshua is correct in that our Sages never enacted this decree in a situation where the Chametz would never be able to add flavor to the mixture.
Nonetheless, Maran Rabbeinu Ovadia Yosef zt”l writes that it is difficult to rely on this reason alone to rule leniently. However, he adds that there is another great reason for leniency based on what Maran Ha’Shulchan Aruch rules that a courtyard where there are birds need not be searched for Chametz, for even if a piece of Chametz was left over, the birds would certainly eat it. (Although Maran Ha’Shulchan Aruch implements this rule only with regards to doubtful Chametz, nevertheless, here there is even more room for leniency.) Based on this, in the Kinneret where it is almost certain that the fish eat whatever is thrown into it quickly, there is no reason to be concerned about any Chametz mixture.
Furthermore, there is even a disagreement among the Poskim as to the validity of the law that Chametz on Pesach is not even nullified by a ratio of one to one-thousand, for according to the She’iltot of Rav Achai Gaon and the Ba’al Ha’Ma’or, Chametz, even on Pesach, is nullified by a ratio of one to sixty like all other forbidden foods.
With all of these reasons (and several others) combined, Maran zt”l rules that there is room for leniency regarding drinking water from sources contaminated by small amounts of Chametz on Pesach (see Yabia Omer, Volume 7, Chapter 43).