Well Poisoning Accusations in Medieval Europe: 1250-1500
In late medieval Europe, suspicions arose that minority groups wished to destroy the Christian majority by poisoning water sources. These suspicions caused the persecution of different minorities by rulers, nobles and officials in various parts of the cont...
Did all historical Christian writings at the time blame Jews? I doubt that and I'm sure it was very few. The idea just sounds unlikely that Jews could manage to poison so many wells across Europe (and Asia) and avoid screwing themselves in the process.