Pinellas County Sheriff Bob Gualtieri said an operator managed to catch the manipulation in real-time and restored the concentration levels to undo the damage. The water treatment facility, which is located in the city of Oldsmar and serves about 15,000 residents, is said to have been breached for approximately 3 to 5 minutes by unknown suspects. The attacker briefly increased the amount of sodium hydroxide from 100 parts-per-million to 11,100. In high and undiluted concentrations, it can be toxic and can cause irritation to the skin and eyes.
Source: https://thehackernews.com/2021/02/hacker-tried-poisoning-water-supply.html