At this point you almost have to take it as certain that, if they ever want to, china can shut of the lights and water at many, many places in the US. They plan far, far ahead and there are too many reports of intrusions into power grid-related networks to assume otherwise.
if the US ever tried to militarily stand-up to china, i think their planning has to assume this capability plus who knows what penetration of military networks, PLUS the ability to temporarily re-route a big chunk of world internet traffic through their servers and filter/block whatever they want (they demonstrated this).
An analogy I like is that the Chinese government is playing chess against the US, and the US is playing tic-tac-toe against itself, with china directing one team anyway.
There is speculation that the brazilian power failure some time back was actually either a test or a test that wasn’t supposed to go live, by whoever penetrated their network.