Often times, dishwashers will start their wash cycle by draining the standing water in the bottom of the dishwasher. The dishwasher will send power to the inlet valve and the homes water pressure will send water through the dishwashers inlet hose to it's tub.
Some Common problems
An inlet valve can experience various problems.
Sometimes for various reasons The hoses in the dishwasher will develop leaks
In area with hard water calcium may build up and either clog the valves filter mesh or prevent the solenoid from firing correctly. Vinegar or other acidic cleaning solvents can normally remove the build up for a temporary fix but replacing the part is recommended.
The Inlet valve may fail electronically. One way of testing this is to use a multimeter to test it's resistance. Different inlet valves have varying expected resistances. Many inlet valves have resistances between 500 and 1500 ohms.
It should also be noted that the Inlet valve need a certain amount of water pressure to work properly. The exact number varies depending on the part and dishwasher however most dishwasher inlet valves operate between 20 psi and 120psi.
It is recommended to replace the part the at has developed the leak.