You can use the water after you let it boil for a full minute.
Already I've messed up. Spouse bought some of the last bottled water, and I carried a glass into the bathroom to brush my teeth, but it was second nature to rinse the brush off with the tap.
And then you stare at your toothbrush and wonder what to do next. Boil it? Rinse it with bottled water? Toss it?
I ended up hitting it against the side of the sink and continuing on.