While You Wait for the Truck
Shut the main water valve before anything else. 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.
Standing water and live outlets are the biggest danger 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.