While You Wait for the Truck
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. Next head to the panel, but only if you can get there on dry footing.
Water on the floor plus energized outlets is the hazard that hurts people on these calls. If water is touching outlets, cords or a power strip, stay out of that room and tell the dispatcher. 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.