why does a contaminated water supply only require warnings for the area near it, and not all the places it supplies to?

Question

a few months back there was contaminated water found in the west part of my county. it had the same water supply as the entire county, however there was only a boil water advisory for the area it was found in. why is that? apologies if this is worded incorrectly, especially the title

In: 1

Answer 1

Often this contamination comes from the underground pipes that carry water to your house, not from the source. In this case only the people after that part of the pipe will be affected.