Know where the shutoff is before you need it
Find your main water shutoff today, not during a flood. In North Carolina homes it is usually at the meter near the street, in a crawlspace, or where the line enters the house on the side nearest the meter.
Turn it fully closed and open again once a year. Valves that are never operated seize, and a seized main valve turns a manageable leak into a disaster.
Burst pipe or uncontrolled leak
Close the main. Open the lowest faucet in the house to drain pressure out of the system. Cut power to any circuit near the water. Then call.
Move what you can out of the water. Photograph everything before it is cleaned up.
Overflowing toilet
Take the tank lid off and push the flapper down by hand to stop the fill. Close the angle stop behind the toilet.
If it overflows again when another fixture drains, do not keep plunging - the blockage is in the main line.
Sewage backing up
Stop using every fixture in the house immediately. Everything you run adds to what is coming back up.
Keep people and pets out of the affected area. This is one to treat as urgent rather than wait until morning.
Gas smell
Leave the building first. Do not use switches, phones or anything that could spark, and do not go looking for the source.
Call the gas utility and a plumber from outside. If the meter shutoff is on your way out and you can operate it safely, close it.