Some pathogens can cause disease with only a few.

Most importantly, the water test for biological contamination mainly uses E. coli number per militer. We know there are one to tens of billian bacteria in one gram of feces. The bacteria will grow very quick after the death of the pigs. We do not know exactly what kind of bateria and how many of them getting into the drinking water. We do not know what is the effects of these bacteria on the diseased or immunocompromised people. How can we conclude that it is OK even with a few thousands of dead pigs floating drinking water resource?