Well poisoning
Well poisoning is the act of malicious manipulation of potable water resources in order to cause illness or death, or to deny an opponent access to fresh water resources. Well poisoning has been historically documented as a strategy during wartime since antiquity, and was used both offensively (as a terror tactic to disrupt and depopulate a target area) and defensively (as a scorched earth tactic to deny an invading army sources of clean water).