I found this story very interesting and also tragic, but just wanted to clarify -- yellow fever isn't contracted by drinking tainted water. It's contracted by a mosquito bite from an infected mosquito:
http://en.wikipedia.org/wiki/Yellow_feverYou didn't mention what time period this happened and medical science wasn't as advanced as it is today so it was probably thought that the water was contaminated with yellow fever when, in fact, there was probably a high concentration of mosquitoes in the area.
Just my thoughts......