I wrote on the subject of cyber warfare and the vulnerability of our nation's utilities first in 2015. At that point, a single malicious actor had gained access to a water treatment plant in Chicago that had no air-gap. They were able to cripple a system by turning a key portion on and off until it burnt out. In 2016, a water treatment plant was targeted in an attack which released high levels of treatment chemicals into the water supply. There is an exceptionally high risk of damage.

https://www.infosecurity-magazine.com/news/water-treatment-p...

From the glimmers of info we do have about these things, most situations that involve them we either don't know about or involve brinksmanship. See here for reference: https://arstechnica.com/tech-policy/2016/02/massive-us-plann...