I know a guy who owns a retired nuclear missile silo that he made into a doomsday bunker/business. The top several floors or so with the old control rooms and stuff has been converted into his bunker, but most of the main silo is flooded with water, so it's a scuba diving attraction.
Anyway: when Covid came his bunker and years of food and fuel, so he and the wife went out there and used it for their lockdown. I'm happy for him that he got to use it.
They took out the old control rooms and completely remodeled the inside into a pretty comfy house. It's just underground and has 3-ton blast doors.
It's basically aquifer water. When the silo was active they had to run pumps to keep it from flooding. It's actually one of the ways silos could be identified by satellites. They'd have oversized drainage ponds in the middle of nowhere where they'd be pumping the water.