A clogged toilet should be treated in much the same way as a blocked drain, with the exception of a few minor details. If a toilet overflows, you should stop the flow of water by reaching inside the toilet tank and pushing the tank stopper down into its valve seat. Hold it until the tank fills and the water stops. Next, turn off the shutoff valve underneath the toilet or turn off the main water shutoff valve. Unclog the toilet. Due to the fact that the trap is built into the toilet, if you are unable to unblock the drain with a plunger, call a plumber.
There are several types of plumbing emergencies that can occur, but the first step in all solutions is to turn off the water in the supply line that feeds the leaking pipe or fixture. If it happens that the point of the leak is hidden or there is no valve in the branch line leading to the leak, you will have to shut off water to the entire house.
If you live in a climate where there is a danger of freezing, the main shutoff valve is usually located in the ground floor. In warmer climates the valve may be located outdoors. If you have a pumped well system, shut off electricity to the pump and call a plumber.
In a case where you are unable to close the shut off valve, contact your local water authority immediately, so that water can be turned off at the main. If the water rises to the level of electrical cords and outlets, there is a possibility that it could be carrying an electrical current. Do not attempt to go near the water until you shut off electricity to the circuits affected. If you are unable to reach the breaker or fuse panel safely, have the power company shut off the electricity to your home.