Do These Things While Help Is Coming
Close the main shut-off first. If you cannot find it or it will not turn, the curb stop near the street can shut the supply, though it may need a special key. Then go to the breaker panel, but only if you can reach it without standing in water.
Water on the floor plus energized outlets is the hazard that hurts people on these calls. If the water has reached outlets, extension cords or electronics, keep out of the room and let the dispatcher know. Move valuables, documents and medications upstairs or onto high shelves.
Dispatcher tip: Tenant with a landlord who is not answering? Shut off the water, take photos, and text and email the landlord with the time, so there is a record that you acted quickly.