Could you elaborate more please? (:
I would say that <u>a deadly water-borne microorganism in a city's water source</u> would most quickly devastate a human population, merely because a huge number of people uses this water for some kind of a purpose.
When Pasteurization was first invented many people could and would become ill to certain products due to tainting with certain bacteria and fungi. Additionally these various bacteria would cause the taste of these products to sour.
Originally Pasteur would come up with the method of heating up a certain food or substance, to kill these pathogens, when working to improve the longevity and taste of Wine. His method however is now used around the world for use in purifying Milk and Dairy, Wine, fruit juices, etc... and reducing the risk of food poisoning, while also improving the economics of these products.
Identifying your limitations because you’re taking risks to KNOW the limits of yourself.