A dishwasher usually has a dedicated shut off valve on the water pipe leading to the machine. The main water pipes under the sink may have a horizontal pipe branching off that runs to the dishwasher. This pipe should have a shut off valve on it.
The dishwasher shut off valve lets a homeowner quickly shut off the water supply to the appliance. If the dishwasher malfunctions, using the shut off valve can reduce water damage to the home. The valve is also useful when replacing the dishwasher. Instead of turning off the water supply to the entire house, homeowners can use the valve to only stop water flow to the dishwasher.