Today, I noticed that a restaurant I manage had its OpenTable booking integration replaced with Google Assistant.

Replaced in what context? My understanding is that OpenTable still works just fine but Google is, on its end, no longer automatically referring its own users to OpenTable. I wouldn’t call that “hijacking” unless the restaurant had a prior agreement with Google.

No Available Reservations

That’s not the error message. Google says that you can’t get a reservation through Google Assistant not that there are no reservations available.

19, because I started going bald very early. I’m about 40 now.

Whole home water filters is what you want.

My well water had arsenic in it and I installed a filter only on the cold water line to the kitchen sink. I only drank that water and unfiltered water was fine for everything else. Something like that could be much cheaper for OP.