Sewage holds toxic microbes and contains a mixture of suspended impurities. When these impurities hit drinking water microorganisms begin to deteriorate the water, and uses up the dissolved oxygen with the microorganisms, making these water dangerous to drink from. Major impacts of this can include giardia, salmonella, cryptosporidium, and E. coli.
A group of similar cells that perform a single function is called a tissue.
I might be concerned about the milk because it has been modified, but If the cow is completely healthy, than the milk should be fine, too. My only concerns would be if the genetic modifying might effect the milk in a strange way.
