Apparently the water.. is not well.
There was an episode of Doc Martin (PBS, great Show) where people in town were afflicted with Diarrhea.
At first the Doctor thought the link was the local Swimming Pool and pissed off the guy who ran it.
Then he suspected the Local Water Supply and caused a panic.
Turns out it was a guy selling bottles of French Spring Water. The Doctor found out when he caught the “mislabeled” Bottles being filled by the guy using his own Spring, which happened to fed by Water from a Pasture area full of Farm Animals.