What happened

A plant operator reported seeing the sodium-hydroxide dosing setting on Oldsmar's water-treatment control system remotely raised from about 100 parts per million to 11,100 parts per million. The operator immediately reversed the change, independent process safeguards remained in place, and officials said no unsafe water reached the public. Authorities initially announced the event as an external computer intrusion, and it became a widely cited critical-infrastructure cyber case. Later, however, the FBI said its investigation could not confirm that a targeted cyber intrusion caused it, while the city's former manager said employee error was likely. The record is therefore marked investigating and disputed rather than asserting that a hacker attempted to poison the water supply.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.