Running a pressure washer without water can cause damage to the pump and other components of the machine. It can also cause pressure buildup which can lead to damage in various parts of the machine, including hoses, fittings, and connectors. In extreme cases, the pressure can become hazardous, causing bursts or explosions. Pressure buildup can also put excessive strain on the motor or engine. The pump relies on the motor to drive its operation, and without water, the pump encounters increased resistance. This can lead to motor overload, overheating, and potential motor damage.