Why? Water for flushing is nice for hygiene in the most common case of short outages. And there's very little storage annoyance - heck if you need a bucket for a project, you dump it out and fill it back up from the hose when done.

Drinking water requires more expensive containers, and some thinking around keeping it fresh (rotation & potentially some chemical additives like bleach).

Technically that's 60L for flushing.

Not really. Not being able to flush is annoying, but you can do that outside. There are some health risks but they are manageable (human waste carries pathogens). 3 days is a very long disaster: if things are that bad you need to start activating other plans anyway. I wouldn't be surprised if where he lives he can just go to a nearby stream and refill his flush water anytime he wants.

Water is critical to life and so you want to be sure civilization won't return before you risk drinking random water. That said, I'd keep a camping water treatment instead (there are lots of options) since they take up less space.