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 the water has reached outlets, extension cords or electronics, keep out of the room and let the dispatcher know. Get papers, medications and valuables up and off the floor.
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.