Jews poisoning wells

A medieval trope or stereotype of sorts mentioned in the Protocols of Zion

Jews are typically city people or city dwellers who would think of themselves as "citizens" with respect to the Holy City, Jerusalem. Christianity as such traditionally exists mostly outside city limits, as Jesus Christ suffered and died and rose again without the gates according to the Bible.

City Hall has been synonymous with Jews living and working in business and banking districts since medieval times in Europe. And when people accused "Jews" back then, they were accusing city people in general, as there was always a substitute atonement for Jews in a certain manner of speaking.

So the complaints of "Jews poisoning wells" in medieval Europe and Russia (before the German Holocaust and the Russian pogroms) were really only meant to be interpreted as generic complaints about the quality, supply and cost of city water. The term "pogrom" may be a corruption or dialectical variant of "program." Hollerith punched card tabulating machines were then used to compile vital statistics in large cities, and people highly resented being tracked and identified by the government when the computerized equipment was first introduced.

The punched card tabulator | IBM
An electrical counting machine automated data handling, transformed industries, and became the basis for a highly profitable new company called IBM.
America’s drinking water is facing attack, with links back to China, Russia and Iran
The majority of U.S. public water systems are vulnerable to hacks, and cybercriminals are not passing up the opportunity to cause chaos.

It's "the nations" (or "goyim") and not "the Jews" taking the blame in this CNBC article. Nevertheless all attacks on domestic water supply remain a concern.

What Causes Tap Water Contamination
Tap water can get contaminated by human or animal poop, chemicals, or other sources.
EWG’s Tap Water Database: What’s in Your Drinking Water?
Look up your local water system to find out which pollutants might be of concern, and find suggestions on the best kinds of home filters to remove those chemicals.

Conspiracy theories or not, some healthy skepticism of source, quality and cost of domestic water supply (urban or rural) is warranted and justified.