To clarify on R. Hershel Schachter’s pesak:
In my haste, I left out some very important points.
1. The creatures in the water are dead. However, if, when alive, they were identifiable as creatures by their movement then, even when dead, they are still prohibited.
2. R. Shachter “heard” that the majority of specks in Boro Park and Flatbush water are these creatures and are, therefore, forbidden to be drunk.
3. R. Schachter ends with a “however”. The water would be permitted if we are willing to rule based on the following innovative approach: Just like with a Torah scroll, we are not obligated to check each letter with our eyes right up to the parchment but, rather, from the distance of about a foot, perhaps with these creatures also, we should only rule based on observation from a distance. Since we would only have known that these are living creatures because of looking more closely than we are obligated, perhaps they are permitted anyway. R. Schachter leaves this with a “ve-ayen“, because it is difficult to suggest that the Tanna’im and Amora’im did not drink similar water.