Well, there are all kinds of concrete and I'm sure that any concrete enclosure specifically designed to hold water would take that into account.

I'm surprised that you haven't heard this bit of preparedness advice before. I have heard/read it numerous times over the years. I just heard it again when I recently went through my city's 8-week Community Emergency Preparedness Academy program and it was the guest speakers from the local water utility who repeated this advice to us.