DIAGNOSIS An internal hose connection has come loose or a seal has failed. Common leak points are the thermoblock outlet hose or the pump connections.
FIX Unplug the machine. Move it to an empty sink. Remove the rear cover by taking out the two screws. Inspect all silicone tubing connections for leaks or cracks. Push each connection firmly to re-seat it.
IF THAT DIDN'T WORK The leak is likely from the plastic water tank receiver or the internal diverter valve. These parts develop hairline cracks over time. They require full disassembly to replace.
HEADS UP Water inside the chassis can short the main control board. Do not use the machine until the leak is found and stopped. It is an electrocution risk.