Hotpoint's dishwashers had something like this
The Hotpoint impeller dishwasher we found with the hidden timer and push-to-start button had a mechanism next to the timer that measured the current draw on the motor via water resistance against the impeller to determine when the machine was full enough to shut off the water.
In fact, it stymied us from ever getting the dishwasher going after the motor burned out--we couldn't find another GE motor with the correct amp rating, and if it was too low, it flooded--and too high of an amp rating caused the machine to never fill!