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.
In the event that a pipe leaks or breaks, or a joint loosens, immediately turn off the main shutoff valve to prevent water damage. Next, turn off your hot water heater by turning off the circuit breakers and the gas supply to the hot water heater. Failure to do so can cause the hot water heater to overheat, damage the heating elements and injure anyone who unknowingly turns on a hot water tap.
You can either make the repairs yourself or call a plumber. If one of your water-using appliances seems to be leaking, the first thing to check is the trap by which the appliance drains. If it appears to be partially clogged, this could be the problem as it is probably causing an overflow within the appliance. If the drain is clear, consult the appropriate appliance repair person.