While You Wait for the Truck
Shut the main water valve before anything else. If the house valve is stuck or missing, the curb stop out by the street can cut the supply, but it often needs a curb 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? Close the valve, photograph everything, and send a timestamped text and email so it is clear you moved fast.